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A NEW 



SCHOOL PHYSIOLOGY. 



BY 



RICHARD J. DUNGLISON, A.M., M.D., 

Author of "The Practitioner's Reference Book," Editor of 
Dunglison's "Medical Dictionary," "History of Medi- 
cine," Secretary of the American Academy 
of Medicine, etc., etc. 



ILLUSTRATED WITH ONE HUNDRED AND SEVENTEEN 
ENGRA VINGS. 




IA% 



PORTER & COATES 
PHILADELPHIA. 



Copyright, 

PORTER & COATES 

1880. 



PREFACE 



It has been the aim of the author in the following pages 
to impart such information on the interesting subject of 
Physiology as will make the reader familiar with the gen- 
eral structure of his own body. To young people this 
knowledge is especially important and desirable. They 
have the opportunity to be practically benefited by such 
instruction at a sufficiently early period in life to enable 
them to be watchful in regard to the laws of health, which 
they must necessarily study in connection with Physiology, 
Experience as a physician fully justifies the author in the 
statement that it is in ignorance of such laws, and in con- 
sequence of the lack of proper education in this useful 
branch, that so many adults are daily violating the sim- 
plest principles of health. No more important subject 
can be taught in the schools than that which instructs the 
student in the principles of his own formation. In the 
frequent allusion made throughout this work to Compar- 
ative Anatomy and Physiology — the anatomy and phys- 
iology of other animals compared with man — the reader 



4 PREFACE. 

will be able to appreciate the lofty position occupied by 

him in the scale of creation. The knowledge which will 

thus be acquired by him of the higher state of development 

characteristic of man, and of the possibilities of still greater 

perfection of his intellectual and physical powers under 

proper education and training, will be one of the most 

valuable and improving lessons which Physiology can 

teach. 

RICHARD J. DUNGLISON, M. D. 



CONTENTS. 



INTRODUCTORY. 

PAGE 

Physiology and Anatomy Defined 10 

Aids to Physiology 11 

Organized and Inorganic Bodies 12 

Physiology of Animals and Vegetables 14 

Cells 19 

Divisions of the Human Body 21 

THE BONES, JOINTS, AND MUSCLES. 

The Bones 27 

Structure of Bones 28 

The Spinal Column 29 

The Limbs 32 

The Joints 34 

The Muscles 36 

Tendons 38 

Movements 41 

DIGESTION. 

Digestion in the Vegetable 49 

Food of Man 50 

Ingredients of Food 52 

Classification of Food 53 

Oils and Fats 54 

Sugar and Starch 55 

Gum; Albuminous Substances 56 

Animal Food 58 

Milk 60 

Eggs; Vegetable Food ; Bread 62 

Cooking 64 

Drinks 65 

Conditions Necessary for a Healthy Diet 71 

Appetite and Hunger 72 

Thirst 74 

Apparatus for Digestion 74 

1* 5 



6 CONTENTS. 

PAGE 

The Teeth 76 

The Tongue 80 

The Salivary Glands 80 

Deglutition 82 

Processes of Digestion 84 

Digestion in the Stomach and Intestines 86 

Stomachs of Other Animals 91 

Changes in the Food in Digestion 96 

Digestibility of Food 9S 

Digestion in the Intestines 101 

Intestinal Juices 10-4 

ABSORPTION. 

Various Forms of Absorption 120 

Intestinal Absorption • 121 

Lymphatics 12-1 

RESPIRATION. 

Objects; Changes Produced 128 

The Chest and its Contents 130 

The Lungs 131 

The Act of Breathing 134 

Sounds of the Chest 136 

Capacity of the Lungs; The Air-Cells 137 

The Air we Breathe 138 

Ventilation.. 141 

Respiration in Animals Generally 142 

Respiration in the Vegetable 144 

CIRCULATION. 

The Heart 148 

The Greater and Lesser Circulation 151 

Valves of the Heart 152 

Sounds of the Heart 155 

The Pulse 156 

The Quantity of Blood : The Arteries 158 

Pulse-Writing; The Veins 160 

The Capillaries : Velocity of the Circulation 162 

Infusion and Transfusion 163 

Circulation in Other Animals 164 

The Blood 167 

White Corpuscles 171 

Coagulation of the Blood 172 



CONTENTS. 7 

ANIMAL HEAT. 

PAGE 

Temperature of Animals 179 

Effect of Food, etc. ; Temperature of Organs ISO 

Atmospheric Influences, Clothing, etc 181 

SECRETION. 

Materials Separated from the Blood 184 

Glands; Secreting Surfaces 185 

THE NERVOUS SYSTEM. 

Divisions of the Nervous System , 190 

Cerebro-Spinal System 192 

The Brain 193 

Brains of Different Races; Facial Angle 196 

Cerebellum; Spinal Cord 199 

TheNerves 200 

Great Sympathetic Nerve 20S 

Functions of the Nervous System 210 

Functions of the Nerves 211 

Reflex Action of the Spinal Cord 212 

Functions of the Medulla Oblongata 214 

Functions of the Cerebellum 215 

Functions of the Cerebrum 216 

Phrenology; Sleep ." 218 

Nervous System of Animals 221 

THE SENSES. 
Their Objects, etc 231 

Taste 

The Organ of Taste 233 

Nerves of the Tongue 237 

Organ of Taste in Other Animals : 238 

Smell. 

The Organ of Smell 240 

Odors.. 242 

Sense of Smell in Animals 244 

Touch. 

The Organ of Touch 247 

The Skin 248 

The Papillae 249 

Sweat-Glands 250 



8 CONTENTS. 

PAGE 

Sebaceous Glands 251 

Hair 252 

Color of the Skin 253 

Sense of Touch in Animals 256 

Vision. 

The Sense of Vision 258 

The Organ of Vision ; Protection of the Eye 259 

The Tears 260. 

The Orbits; The Eyelids 26] 

The Eyelashes; Transparent Parts of the Eye 262 

Coverings of the Eye 264 

Motions of the Eyeball 266 

Light 267 

Image on the Retina 270 

Accommodation of the Eye to Distance 271 

Perception of Colors 275 

Vision in the Inferior Animals 276 

Hearing. 

The Apparatus of Hearing 282 

External Ear; Middle Ear 283 

Internal Ear 283 

Functions of the External Ear.. 285 

Functions of the Middle Ear 286 

Functions of the Internal Ear 287 

Sound 288 

The Sense of Hearing in Other Animals 289 

VOICE. 

The Organ of Voice 293 

The Larynx 293 

The Vocal Cords 294 

Muscles of the Larynx 295 

Production of Voice 296 

The Singing and the Speaking Voice 299 

The Formation of Language 300 

Vocal Apparatus of Animals 303 



PHYSIOLOGY 



It was formerly the custom to divide all bodies into the 
three classes. Animals, Vegetables, and Minerals, and this 
mode of division is still adopted by some writers. Animals 
and vegetables resemble each other, however, in so many 
respects, especially in the possession of organs, that it has 
seemed desirable to make a different classification. The 
division now generally adopted is into organized bodies 
and inorganic, the organized being composed of organs 
for the performance of certain duties, while no such ar- 
rangement exists in the inorganic. Animals and vege- 
tables, being made up of organs, belong to the class of 
organized bodies ; minerals are inorganic. 

Physiology proper. — Physiology is that branch of science 
which treats of the healthy exercise of the various organs 
of the body. It is derived from two Greek words denoting 
the doctrine of nature. Vegetable Physiology examines the 
properties of vegetables only, in all that concerns their life 
and nourishment. When the term Physiology is used alone, 
it is generally understood as restricted to man and animals. 
It is called Human Physiology when applied to man alone ; 
it is known as Comparative Physiology when applied to 
animals generally as compared with man. 

The chief subject of our inquiry will, of course, be the 
physiology of man, but allusion will frequently be made to 
comparative physiology, so that the place occupied by man 



10 PHYSIOLOGY. 

in the scale of animals may be thoroughly understood. In 
whatever department we study physiology, we cannot fail 
to be struck with the vastness of its scope, for it embraces 
a knowledge of the progress and decay of all forms of 
vegetable and animal life, from brute matter, which is 
devoid of vitality, to the most perfect animal — man him- 
self — who possesses it in the highest vigor. 

Anatomy. — Anatomy is a distinct branch of inquiry, and 
is derived from a Greek word meaning dissection, but as 
generally used signifies that study by which, through the 
medium of dissection, we become acquainted with the struc- 
ture of the several parts that enter into the composition of 
the bodies of animals. It is really necessary, as a general 
rule, to understand the structure of the various organs of 
the body — that is, their anatomy — before we can fully appre- 
ciate their physiology. We can sometimes infer from the 
anatomy of a part what are its uses, but some of the organs, 
such as the brain, giye us but little information. We know 
that there can be no exercise of intellect without a brain, 
and yet when we come to examine that important organ we 
learn absolutely nothing from its structure. It is appar- 
ently only a mass of fat, phosphorus and other chemical 
materials arranged in a peculiar way and protected from 
injury in a bony covering. 

This is all we learn from its anatomy or chemistry, 
although it is an organ capable of the highest duties 
and has many important organs under its control. An- 
atomically, the eye is a perfect organ and the structure 
of the tongue is very familiar to us, yet the nicest dis- 
sector has failed to show us how the eye possesses the 
power of giving us our ideas of external objects or the 
tongue can impart to us the hundreds of varied flavors. 

Comparative Anatomy is the study of the structure of 



PHYSIOLOGY. 1 1 

other animals than man as compared with him. When 
we see differences in the arrangement of their organs we 
know that there must be some different duty performed, 
and thus we may acquire a knowledge of their physiology. 
For instance, we see a variation in the anatomical arrange- 
ment of the stomachs of animals, and this we find occurs 
in accordance with a variation in the kind of food they 
live upon and the amount of digestion required. 

Aids to Physiology. — Even disease or malformation may 
aid us in learning physiology. Cases have occurred where 
life was carried on for a while without any brain, the child 
breathing and swallowing just as well without it, although 
it would not, of course, exhibit any mental power. This 
shows that the acts of respiration and of swallowing are 
not controlled by the brain, and so by the absence of an 
anatomical part we derive information negatively as to its 
duties. 

The laws of Physics are also involved in the study of 
physiology. Sight or vision is an example of this, the eye 
being mainly a physical apparatus, a transparent body 
influenced by the laws of light. If the physical part be 
imperfect, vision is defective. So, too, the muscles are a 
physical apparatus, acting like levers of different kinds 
according to the angle or mode in which they are inserted 
into the bones. As we shall see hereafter, the arrangement 
of the ear for hearing is partly a physical apparatus. 

Chemistry also aids us in the study of physiology. 
Digestion, for example, is mainly a chemical process, the 
juices in the stomach and small intestines which effect it 
being made up chiefly of acids and a ferment. The fluids 
in the mouth which act on the food in that cavity produce 
their effect by chemical action. Respiration or breathing 
is also a chemical and mechanical process, being an ex- 



12 PHYSIOLOGY. 

change of gases into and out of the lungs, oxygen being 
received into those organs, and carbonic acid being given 
off. These functions or processes are also, to some extent, 
affected or regulated by a nervous system. There are many 
functions that are performed wholly or in part in a me- 
chanical or chemical manner, and their action is easily 
understood ; yet the controlling power — the vital action — 
is wholly beyond our calculation. The healthy action of 
the heart, for instance, is dependent on the movement of 
its own muscles and of valves in its interior, which act in 
a purely mechanical manner; and yet we cannot explain 
minutely why such action is carried on through life and 
sometimes by artificial stimulation after death. Vie say it 
is a power existing within itself, under proper control, and 
there our explanation ends. 

Differences between Organized and Inorganic Bodies. — 
Inorganic bodies, such as minerals, are not born, as animals 
are ; they do not possess life, and have not a certain definite 
shape like animals and vegetables. In each of these last — 
the animal as well as the vegetable — there are a particular 
form and recognized size, which belong to that kind and to 
every part of it. Vegetables, for instance, have a certain 
relation of size and shape of their stems and roots and 
limbs ; and animals have their bodies and all their parts 
framed on one general and uniform plan. The animal 
and vegetable are constantly undergoing change, while the 
mineral is at rest. As long as life lasts the organized body 
is never in perfect repose; it is continually receiving food 
in some shape or other with which to support life, or car- 
rying on the circulation of blood or of some other fluid 
necessary to its existence, or performing some other duty 
assigned to its various organs. In the animal and vege- 
table the different parts have a certain dependence upon 



PHYSIOLOGY. 1 3 

each other, and no portion can be detached from another 
without inflicting injury upon the whole body ; but large 
pieces can be broken from a mineral, and its shape entirely 
changed by force applied to it, without any such sympathy 
on the part of the rest of the body. When we examine 
the structure of these different classes of bodies we find a 
great variation, for, as already stated, animals and vege- 
tables have a regular uniform arrangement, and certain 
parts which serve as organs. These are known by definite 
names : in the vegetable, for instance, they are the roots, 
leaves, flowers, bark, etc. ; in the animal, the nerves, 
muscles, blood-vessels, etc. In a mineral or inorganic sub- 
stance the structure is alike throughout. In the animal 
or vegetable, as we shall hereafter see, the particles are 
arranged in the form of fibres which run in all directions 
through and across one another to form a tissue, through 
which the different organs are made up. 

Organic bodies pass through a series of changes, which 
in the animal particularly are known as ages, during which 
the organs become developed, attain their full growth, and 
then decay. The condition of the inorganic body is very 
different ; it only changes its color or its shape when 
affected by the influence of blows or external agents, as 
rain, etc. A stone may increase in size by the addition of 
earthy or other matter to its surface, but it never grows 
in the same sense that animals and vegetables are said to 
grow. 

So, too, with regard to the death of either of these 
organized bodies ; they generally cease to have life as the 
result of some cause operating from within, as when a 
vital organ — the heart or lungs, for example — becomes 
diseased and unable to carry on its duties. The inorganic 
body has no death ; it may be broken to atoms by force, 

2 • 



14 PHYSIOLOGY. 

or it may crumble into dust, but there is no cessation of 
life here, for actual life never existed. Some of the lower 
forms of animals and vegetables may exist but a short 
time, while man may sometimes live a century ; but this 
short or long duration of life is controlled by the interior 
organization of the animal and by external causes operating 
upon it. 

AVhen the organs of the animal perform the work 
assigned to them properly and in full vigor, they are said 
to be healthy, and the general condition is said to be one 
of health. The reverse of this, when the action of the 
organs is interfered with from any cause, is called disease. 
The term hygiene has been applied to that branch of study 
which includes all the different methods, medical or other- 
wise, devised for the preservation of health ; for Hygeia, 
in the ancient mythology, was the goddess of health. 

Differences between Animals and Vegetables. — It is not 
so easy to draw the line here as it was between these two 
classes of organized bodies and the inorganic. Both ani- 
mals and vegetables require nourishment, and hence we 
say that nutrition is a function or performance common to 
both. But animals have a sense of feeling — sensation — 
which vegetables do not have, and they also have the 
power of moving at their own pleasure, and this is called 
voluntary motion. Under this action of the will they are 
able to move any part of the body as they may wish, or to 
go from place to place in any direction they may desire. 
Some of the lowest forms of animal life seem little higher 
in the scale than the vegetables they resemble, but the 
physiologist has certain laws by which he is able to distin- 
guish them. As a general rule, vegetables contain more 
solids than fluids ; in the animal, as man, although exter- 
nally, to the ordinary observer, largely solid, the fluids 



PHYSIOLOGY. 15 

contained in the various tissues and organs of the body are 
greatly in excess. In the vegetable there is but one ele- 
mentary tissue observable in its structure, a tissue made up 
of areolae,, or spaces, and hence called areolar tissue. The 
animal possesses this, and in addition other primary tissues, 
such as the muscular and nervous tissues, all of which will 
be described hereafter. The vegetable, having no powers 
of sensation or feeling, or voluntary motion, does not re- 
quire a brain or nervous system, or even muscles which 
either a brain or nervous system can control. 

When we say that animals and vegetables present these 
general differences in their structure, we must not forget 
that in the lowest forms of animal and vegetable life such 
distinctions are not perceptible. Some vegetables of this 
kind contain more fluids than solids, and in some of the 
minute animals there is a total absence of muscles and 
nerves, and even of organs, as heart, lungs, or stomach, 
and of vessels to convey the fluids from one part of the 
body to another. When flowers open or close they do so 
under the influence of light or air, or of some other cause 
not requiring a brain or nervous system to produce it. In 
the " sensitive plant/ 7 as it is called, the leaves collapse 
under the slightest touch, but this is merely a power of 
contraction not dependent v>n a nervous system. 

Nutrition of Animals and Vegetables. — So far as nutrition 
is concerned in animals and vegetables, there is observable 
a marked difference. The source of supply of food to the 
vegetable is the earth which surrounds it and in which it 
is firmly fixed. The food thus offered it does not require 
preparation ; it is ready for use, and it is at once absorbed 
by the vegetable. Whatever the animal needs to sustain 
it must be taken into the stomach and digested, as it is 
called, or prepared for absorption for its nourishment. In 



16 PHYSIOLOGY. 

both animals and vegetables absorption of the food is 
necessary before it can be of any service in maintaining 
life ; but the higher classes of animals also have the power 
of seizing upon their food, of moving to obtain it, and, as 
already stated, a will to govern them in their movements. 

Chemical Composition. — As a rule, vegetables are mainly 
composed of the three chemical substances, oxygen, hydro- 
gen, and carbon ; animals have all these, and nitrogen in 
addition, a fact which may be shown as follows : 



Animal. 



f Oxygen, 
Vegetable ' Hydrogen, 

{ Carbon, 
Nitrogen, 

This is not wholly true of either animals or vegetables, 
for the green parts of vegetables are made up of the four 
elements, and the fatty parts of animals of the three ele- 
ments only. This explains why in cases of excess of fat 
in individuals animal food is given as a means to reduce it, 
rather than starchy matter or sugar, which are made up of 
the three elements, for these last would only increase the 
evil which it is attempted to remedy. 

In addition to the four elements just mentioned, many 
others are found in the animal tissues. Some of the prin- 
cipal of these may be conveniently arranged in a table, 
which gives at a glance the particular parts of the body in 
which they have been detected. It will be observed that 
the most important of these are found in all the tissues 
and liquids, while others have a special location : 

Name. Where Found. 

Hydrogen In every tissue and fluid. 

Carbon In every tissue and fluid. 

Nitrogen In many of the tissues; in solution in fluids. 

Oxygen In all the tissues; in solution in fluids. 



PHYSIOLOGY. 17 

Name. Where Found. 

Sulphur Albuminous substances ; blood; secretions; serum of the 

tissues.* 
Phosphorus.. ..Blood; nervous matter ; bone; teeth; fluids. 

Chlorine Tn every tissue and fluid. 

Sodium Blood ; all the secretions; serum of the tissues. 

Potassium Muscles; red blood-corpuscles; nervous matter; secretions. 

Calcium Bones and teeth ; fluids. 

Magnesium. ...Bones and teeth; fluids. 

Lithium Muscles; blood; milk. 

Iron Coloring -matter of the blood; bile; chyle; lymph; 

sweat, etc. 

These simple chemical elements are combined to form 
other bodies or materials of which the various animal tex- 
tures are composed. Water is one of the most important 
of these. The chemical composition of a living being 
varies in quality and quantity at different periods of its 
growth. The seed, for example, differs chemically from 
the plant ; the egg from the grown animal. The quantity 
of water gradually diminishes also as life advances. It 
usually forms about two-thirds of the weight of the body. 
In a person weighing one hundred and fifty pounds there 
are about one hundred pounds of water. It is distributed 
through the body in the most important organs as follows, 
in each 1000 parts : 

Tissues or Organs. Water. Solid Parts. 

Enamel of the teeth 2 998 

Bone 220 780 

Fat 299 701 

Cartilage 550 450 

Liver 693 307 

Spinal cord 697 303 

Skin 720 280 

Brain 750 250 

* By secretions are usually meant fluids separated from the blood, as 
the sweat, the tears, etc. ; by the serum of the tissues, the thin watery 
portions that bathe their surfaces like a moisture. 
2* B 



18 PHYSIOLOGY. 

Tissues or Organs. Water. Solid Parts. 

Muscles 757 243 

Blood 791 209 

Bile 864 136 

Milk 891 109 

Chyle 928 72 

Gastric juice 973 27 

Tears 982 18 

Saliva 995 5 

There are also in various parts of the body, as in the 
gastric juice, bones, muscles, blood, bile, etc., acids, such as 
muriatic, sulphuric, phosphoric, lactic, carbonic, and other 
acids ; alkaline substances, such as soda, potassa, magnesia, 
and lime ; salts of various kinds, such as phosphate of lime, 
chloride of sodium, or common salt, etc. ; sugars, such as 
sugar of milk ; fats, as in the oily part of milk ; coloring- 
matters, as in the blood and bile ; and albuminous matters, 
which we shall hereafter find to be present in the blood, 
milk, brain, muscles, and other important solids and 
liquids. The white of egg is the best example of albumen, 
and like albuminous substances in the various parts of 
the body is coagulable by heat, a fact familiar to all in the 
appearance of the egg when boiled. Vegetable albumen is 
the name given to it when found in the juices of plants. 
In milk it is called casein e ; while in peas, beans, etc., and 
in the grains of similar plants, it is called legumine. The 
albuminous body formed during the coagulation of lymph 
and blood is called ftbrine. In the red globules or cor- 
puscles of the blood there is an albuminous body called 
globuline ; and when the albuminous matters in the 
stomach are acted upon by the gastric juice, a substance 
called peptone results. 

In addition to all these and other substances in the 
bodies of animals, certain airs or gases are found. The 



PHYSIOLOGY. 19 

air that passes into the lungs when we breathe is mainly 
composed of oxygen and nitrogen. From food and drink 
taken into the stomach we derive such gaseous matters as 
are found in that organ or in the intestines. The principal 
gas given off from the lungs is carbonic acid, which comes 
from the breaking down of the tissues, and has its outlet 
from the system chiefly at that point. 

Cells. — All the tissues and organs of the body originate 
from a minute form called a cell, which divides into other 
cells, and these, by uniting together, are developed into 
tissues. Organs are made up by a combination of tissues. 
Several organs grouped together form a system or appa- 
ratus. In the apparatus of digestion, for example, there 
are several organs, such as the stomach, intestines, etc., 
which are made up of different kinds of tissues. 

The cells are small vesicles, only visible under the micro- 
scope, composed of a very thin membrane called a cell-waff, 
and contain a semi-fluid matter, in which is frequently 
imbedded a minute oval body called the nu'cleus, itself 
containing sometimes an even smaller body, the nucleolus. 
So that we may correctly say that the nucleolus is the very 
lowest form in which a tissue is capable of being expressed. 
To give an idea of the size of the cells, it may be stated 
that some of the smallest of them are so very minute that 
12,000 of them placed together would only occupy the 
space of an inch. They are of course only visible under 
the microscope. Fluids pass through the walls of these 
cells so readily that the latter may swell when brought 
into contact with thin fluids, while they may shrivel up if 
their own contents pass out into a thicker fluid around 
them. 

Where Nutrition is Effected. — It is in these cells that 
the nutrition of the body is effected. They are found in 



20 PHYSIOLOGY. 

the vegetable as well as in the animal. The cell receives 
certain materials from the surrounding medium, and con- 
verts them into its own substance or makes use of them 
for nutritive purposes. Certain cells have a power of 
selection by which special kinds of material are formed. 
Some cells, for instance, form coloring matter, some fatty 
matter, etc. They make this selection or choice as per- 
fectly as if they had a mind of their own to control them. 
The cells are endowed with special qualities by which they 
perform certain actions when stimulated. Thus a cell of a 
muscle contracts when it is stimulated ; the cell of a gland 
pours out, or secretes, as it is called, a fluid, — that of the 
perspiration or the tears, for example; and a nerve-cell 
takes on itself an action which results in sensation or intel- 
lectual power or exercise of the will. Each cell has a life 
of its own separate from all those which surround it ; but 
the life of the whole body is made up of the lives of all 
the cells which compose it. Some cells die after a few 
hours ; others may exist for years. The cells on the sur- 
face of the body, for example, are being constantly re- 
moved and renewed, while those of cartilages, structures 
which have not much vitality, may endure for a long 
time. The importance of cell-agency in the nutrition of 
. the various organs must not be under-estimated because 
these bodies are microscopic. 

Some of the important cells of the body, as the nerve- 
cells, blood-cells, or corpuscles, etc., will be alluded to 
hereafter when we come to describe the nervous system, 
the circulation of the blood, etc. The solid fat of the 
body is contained in separate cells with delicate walls, 
called fat-cells or adipose-cells. They are globular in 
shape, but become many-sided when pressed together, and, 
although usually larger, are often as small as the -g-oVo^h 



PHYSIOLOGY. 21 

of an inch in diameter. Some cells, known as pigment- 
cells, contain a coloring-matter in their interior, and are 
found in certain parts of the eye and on the skin. They 
are concerned in producing the different colors of the races 
of mankind, and in the eye they have the effect of assist- 
ing in absorbing the rays of light, like the dark parts of 
the interior of a telescope. 

Divisions of the Human Body. — When we study the 
human body in its various parts and structures, we find 
it made up of a number and variety of organs. The frame- 
work is the skeleton (Fig. 1), which is composed of more 
than two hundred bones. The skeleton has at its upper 
part the skull (Fig. 2), which is itself a collection of bones 
of all sizes, fitted accurately together, containing in its 
interior the various portions of the brain. Continuing 
downward from the skull, which is carefully poised upon 
it, is the spinal or vertebral column, or spine, which is a 
series of bones, in the interior of which is the spinal 
marrow. At the lower part of the spinal column, on each 
side, are large expanded bones, called the pelvic bones or 
pelvis, from their resemblance to a basin, as their Greek 
derivation implies. The sides of the pelvis form the hips. 
The framework of the upper and lower limbs is also bony, 
being composed of bones of various sizes adapted to the 
useful movements of those parts. These bones, which 
make up the skeleton, are covered with muscles, which 
give motion to the various portions of the body. Em- 
braced within these various walls formed by bones and 
muscles are the important cavities of the body — the head, 
chest, and abdomen — in which the organs concerned in 
sensation, respiration, circulation, digestion, etc., are placed. 
In the skull is the brain, and in the face, which is the 
front portion of the skull, are the organs of sight, smell, 



Skull 



Spinal column 
Collar-bone. — , 

Shoulder-blade. — , 
Breast-bone 
Ribs 
False ribs 



Vertebral 
column 



Pelvis 

Sacrum 
End of 
spin 



Radius. 




Bones of 
- ankle 
' and foot. 



PHYSIOLOGY. 



23 



taste, and hearing. In the chest, or thorax, as it is called, 
are the heart and kings ; in the abdomen are the digestive 
organs, in which the food is acted upon and absorbed for 
the use of the system. 

In addition to the bones and muscles and the important 
organs just referred to, there are numerous bloodvessels, 




Fig. 2. — Bones of the Skull. 



conveying blood from the heart, to all parts of the body, 
and back again to the heart, and called arteries and veins ; 
and also a set of vessels in every region, called lymphatics, 
which convey a thin fluid, called lymph, to be mixed with 
the blood. Delicate cords, called nerves, greatly varying 
in size, pass everywhere throughout the system, like tele- 
graph-wires, keeping up a communication between the 
brain, spinal cord, and every portion of the body. Cover- 
ing the whole mass of muscles, bones, vessels, and nerves 
is the skin, the sensitive envelope which protects and 
shields the whole bodv from external irritants. 



24 PHYSIOLOGY. 



QUESTIONS. 

Inter what three classes have bodies been divided? 

In what respect do two of these classes resemble one another? 

What are organized bodies? Inorganic? 

To which class do animals belong? Vegetables? Minerals? 

How do you define Physiology ? 

What is its derivation? 

What is Vegetable Physiology ? 

When the word Physiology is used alone, to what does it apply? 

What is Human Physiology? 

What is Comparative Physiology? 

What does the study of Physiology embrace? 

What is Anatomy? 

What relation does Anatomy bear to Physiology? 

What information does the anatomy of the brain give us? 

What is its chemical constitution? 

What do we learn of physiology from the anatomy of the eye or 
tongue ? 

What is Comparative Anatomy? 

What assistance does this give in learning physiology? Take the 
stomach as an example. 

What may we learn from disease or the absence of an organ ? Of 
the brain, for example? 

What examples of physical apparatus have we in the body? 

What process is chiefly chemical? 

What part does chemistry take in it? 

In what respect is respiration a chemical process? 

What action has a nervous system in such processes? 

What is the healthy action of the heart dependent upon ? 

How do we explain this continuous action of the heart? 

How do inorganic bodies differ from animals in regard to life, size, 
shape, etc.? 

Why is change necessary to the life of organized bodies ? 

What evidences of sympathy or dependence of different parts have 
we in animals and vegetables? 

How does this differ from the mineral or inorganic substance? 

What are the various organs called in the vegetable? in the animal ? 

How are tissues made up in the vegetable or animal ? 

What is meant by the different ages in animal life? 



PHYSIOLOGY. 25 

Under what circumstances do inorganic bodies undergo change ? 
When does death or the cessation of life occur in organized bodies? 
What is paid of the death of inorganic bodies? 
When are organs said to be healthy ? 
What is disease? 
What does hygiene include? 

What function or process is common to animals and vegetables alike? 
What two functions have animals that vegetables do not possess ? 
Are solids or fluids in excess in the vegetable ? In the animal? 
What is the elementary tissue of the vegetable? 
How does this differ from the animal ? 
Why is a nervous system not necessary to the vegetable? 
What peculiar exceptions are noted in the lowest forms of animal and 
vegetable life? 

How do flowers open and close? The "sensitive plant" ? 
What is the source of supply of food to the vegetable? 
What difference is noted in regard to the animal? 
After taking food, in what process of nutrition do animals and vege- 
tables resemble one another? 

What additional facilities for nutrition have the higher classes of 
animals? 

Of what three chemical substances are vegetables mainly composed ? 
What additional substance is found chiefly in animal tissues? 
What parts of the vegetable are made up of the four elements? 
What part of the animal is composed of the three elements? 
What kind of food should be given to those suffering from excess 
of fat ? 

Why should not starchy or fatty matters be given in such cases? 
State from the table what other chemical elements are found in the 
body. 

Which of those named are found in all the tissues and fluids? 
Select from the table those other elements which are found in the 
blood. In the nervous system. In muscles. In the bones and teeth. 
What special element is found in the coloring-matter of the blood ? 
What do we mean by secretions? By the serum of the tissues? 
What proportion of the weight of the animal body is fluid? 
How much water is there in a person weighing one hundred and fifty 
pounds ? 

What parts of the body are shown by the table to contain more solids 
than fluids ? 

Mention a few important fluids that are very largely made up of water. 
3 



26 PHYSIOLOGY. 

What acids are found in various parts of the body? What alkaline 
substances? What salts? What other chemical substances? 

In what parts of the body are albuminous matters present? 

What effect has heat upon albumen? 

What name is given to this substance as found in the juices of plants? 

In milk and beans what names are given to it? 

What is fibrine? 

What is the albuminous body in the coloring-matter of the blood 
called ? In the stomach as the effect of digestion ? 

How are oxygen and nitrogen taken into the system? 

What is the principal gas given off' through the lungs? 

From what minute form are tissues and organs developed? 

How do organs differ from tissues? 

What is a system or apparatus? 

What is included in the apparatus of digestion ? 

What are cells composed of? 

What is a nucleus? A nucleolus? 

What is the lowest expression of a tissue? 

What is the size of the cells? 

Where and how does nutrition take place? 

What power of selection do cells possess? 

What action takes place when a muscular cell is stimulated? A 
gland-cell? A nerve-cell? 

How long is the life of a cell? 

What is the arrangement of the fat-cells? 

What are pigment-cells, and where do they exist? 

What effect have they on the skin or the eye? 

What is the bony framework of the body called? How many bones 
compose it? 

What is the skull, and what does it contain ? 

What is the vertebral column? What does it contain? 

What are the pelvic bones? 

How are the bones covered ? 

What organs are contained in the front part of the skull ? In the 
chest? In the abdomen? 

What organs are concerned in conveying blood to all parts of the 
body ? 

What are the lymphatics? 

What organs maintain the communication between different parts of 
the body ? 

What general office does the skin perform ? 



THE BONES, JOINTS, AND MUSCLES. 



The Bones. — The general shape and solid form of the 
body depend upon the bones. These act not only as a 
framework for support, but also as a protection to the deli- 
cate organs which they enclose. Some very important 
organs of the senses are thus protected, as the eye and ear, 
within the bony structures surrounding them. The brain 
itself is completely sheltered from ordinary injuries by the 
skull, which, as a bony, air-tight case, covers it at every 
point. The heart and lungs are also similarly protected 
by the bony and muscular walls of the chest. The bones 
are also useful as offering surfaces on which the muscles 
are inserted, for on the bones and muscles thus acting on 
each other depend the movements of the body. The 
important part of the nervous system included in the 
spinal cord is protected by the spine, or spinal column, 
which is a long collection of bones extending the whole 
length of the back. 

The bones are of a great variety of shapes : some of 
them, as those of the hands, are quite small ; others, as of 
the arms and legs, large and capable of numerous move- 
ments. Bone consists of an earthy and an animal part 
resembling gelatin. The earthy part is chiefly phosphate 
of lime, and when bone is acted on by heat and acids this 
is destroyed, and the bone becomes so flexible that it can 
be tied into a knot. This is like restoring it to the con- 
dition it was in when it was first formed, for it was gelat- 

27 



28 PHYSIOLOGY. 

inous before it became encrusted with earthy matter. The 
animal part of the bone imparts to it elasticity and renders 
it tough, while the earthy portion gives it rigidity. The 
earthy matter is in excess in old persons, hence the bones 
are more liable to break at that period of life. 

Cartilage. — Bony matter exists at first in a kind of pre- 
paratory condition called cartilage, the cells of which be- 
come replaced by bony cells, which give to bones their 
particular consistence. Some portions of the body, as parts 
of the ribs, remain during the Avhole period of life in this 
state of cartilage. Where the bones come together to form 
a joint, as in the elbow or knee, the surfaces are in this 
very condition. In the skull, made up of a number of 
bones of different shapes and sizes, no such arrangement is 
necessary. Almost all the bones here fit into one another 
by their opposite edges being bevelled and grooved, so that 
they can be accurately adjusted (Fig. 1. The bones are 
here shown as if widely separated, so that their edges may 
be more plainly seen). The bones of the skull proper are 
not movable, the joints being more like seams, and hence 
called sutures. The lower jaw is the only part that is 
movable, but it is connected with the skull in a different 
manner from that seen in the other bones. 

Division of Bones. — Bones are generally divided into 
long, short, and flat bones. The thigh, for instance, is a 
long bone; those of the skull are flat. Tin's is a good 
division so far as the bones of man are concerned, but 
not of other animals as compared with man, for the same 
bones that we might call long or flat in the one might be 
of very different shape in the other. Some small bones 
are called long, because their structure internally is like 
that of long bones. 

Structure of Bones. — If we examine the interior of a 



THE BONES, JOINTS, AND MUSCLES. 



29 



long bone by sawing through it lengthwise, we are able to 
understand how both strength and lightness are imparted 
to it. It will be seen that it is 
not solid throughout, as might ap- 
pear from an external view of it ; 
but it is divided into two distinct 
portions (Fig. 3) — a hard part, 
which is also porous and honey- 
comb-like at the extremities of 
the bones, and a spongy portion, 
containing in its centre a substance 
called the marrow. When we ex- 
amine the structure of bone under 
the microscope, we notice an ap- 
pearance similar to that presented 
in Fig. 4, the bony mass being 
hollowed out by an immense num- 
ber of small canals, called the 
canals of Havei's, after the anat- 
omist who first described them. 

Through these canals pass the bloodvessels which nourish 
the bone and the marrow contained in it. The bony canal 
is a sort of star-shaped cell, as seen in 
the section represented (Fig. 4). 

The Spinal Column. — This, gene- 
rally known as the backbone, is some- 
times also called the ver'tebral column, 
each piece forming it being called a 
ver'tebra. (The general arrangement 
will be seen by reference to Fig. 5.) 
The various spines, or projections, give 
it the name of the spinal column, by which it is generally 
known. These are readily felt by the hand along the 

2* 



^^»J^S^PH 




1 


■JR 

1* 
Wm 


H 

HB 


■ Piiliiiii 





Fig. 3. — Interior of a Bone. 




Fig. 4, 



*11 
Section of Bone;. 



30 



PHYSIOLOGY. 



am 



a 



Vertebrae of 
the neck. 



Vertebrae of 
the back. 



middle of the back. There are twenty-six bones in the 
chain, smaller at the top of the column, and larger as it 
^.„„ D ^ descends. It is the back- 

bone or groundwork which 
acts as a basis of support to 
the chest and abdomen (Fig. 
6). A canal, called the ver- 
tebral or spinal canal, passes 
through the interior of the 
spinal column, and contains 
the spinal cord, which is one 
of the great nervous centres. 
Between the bones com- 
posing the spine are layers 
of elastic tissue, which give 
to the whole column a slight 
degree of flexibility and 
elasticity without imparting 
much power of movement 
to it. The useful effect of 
this elastic tissue or cartilage 
placed between the harder 
texture of the bones is also 
to diminish the force of 
blows and injuries inflicted 
upon the spine. Were this 
not present, the force of the 
slightest falls or jumps 
would be felt by the deli- 
cate brain as transmitted 
along the solid bony mass 
of the spinal column. The effect may be illustrated by a 
simple and well-known experiment. If a number of solid 



- Vertebra; of 
the loins. 



Fig. 5. — Spinal Column. 



THE BONES, JOINTS, AND MUSCLES. 



31 



ivory balls be suspended by strings parallel with one an- 
other, and the last one of the series be raised and allowed 
to fall against its neighbor, the shock will be communicated 
through all the balls, and the first one in the row will fly 
off at a tangent. If, 
however, one, or per- 
haps two, porous balls 
be placed in the row, 
and the last ivory ball 
be again brought into 
contact as before, the 
force of the blow will 
be so greatly broken 
that the first ball will 
probably remain sta- 
tionary. The elastic 
cartilages between the 
spinal bones yield so 
much to pressure dur- 
ing the day that a per- 
son is actually shorter 
in stature at night 
than he is in the 
morning after a night's 
rest has restored them 
to their natural con- 
dition. 

The relative posi- FlG - 6.— Skull, Spine, etc. 

tions of the spinal column, the skull, and the chest are 
seen in Fig. 6. It will be noticed also that the spinal 
column is firmly planted between two large and irregu- 
larly-shaped bones, called the 'pelvic or nameless bones, 
because they have no special resemblance to any familiar 




Skull. 



Vertebrae of the 
neck. 



Shoulder-blade. 



Dorsal vertebrae. 



Vertebrae of the 
loins. 



Pelvis. 



32 PHYSIOLOGY. 

object. Into the socket or cavity at the side of each of 
these bones is inserted the thigh-bone. This mode of 
insertion of the spine into these bones has been compared 
to the manner in which the mast of a ship is inserted into 
the keelson, and the strong ligaments which connect the 
bones together have been likened to the shrouds which 
bind the mast to the sides of the vessel. The head is con- 
nected to the spine so as to admit of freedom of motion in 
various directions. It was necessary to provide a mechan- 
ism that would allow the head to rotate or turn from side 
to side or to nod, as required. The two upper bones of 
the spinal column are differently arranged from the other 
bones of the series to accomplish this very result. The 
upper bone is called the atlas, for in mythology it was 
Atlas who bore the globe upon his shoulders ; the second 
is called the axis, because upon it the head turns. The 
bony cage (Fig. 6) attached to the spinal column is the 
thorax, which is made up of ribs and the breast-bone, with 
the spine at its back part. Its arrangement and uses 
belong particularly to the consideration of Respiration, or 
the process of breathing, for in the thorax „or chest are 
contained the lungs. 

The Limbs (Fig. 1). — These are known as upper and 
lower limbs. The upper limbs consist of one arm-bone, two 
bones of the forearm — the radius and ulna — and twenty- 
seven bones of the wrist and hand. The lower limbs are 
composed of a nearly similar arrangement of bones, — one 
of the thigh, two of the leg — the tibia and fibula — and 
twenty-six bones of the ankle and foot. The arm-bone, 
generally known as the humerus, moves in the socket of 
the shoulder-blade, a bone which lies on the upper and 
back part of the thorax (Fig. 6). The femur, or thigh- 
bone, as already stated, has its motion in the cavity or 



THE BONES, JOINTS, AND MUSCLES. 



33 



socket of the hip-bone. These bones are all attached to 
one another by bands or ligaments. 

The lower animals differ from man in the number of 
bones, but chiefly in their general arrangement for loco- 




Fig. 7. — Skeleton of Chimpanzee. 

motion or movement from place to place. The stature of 
the chimpanzee, for example (Fig. 7), is not erect like that 
of man, and its skeleton is made to conform to its general 
movements, the bones of its limbs being longer in propor- 
tion than those of man, and aiding in its stooping attitude. 

c 



34 



PHYSIOLOGY. 



We cannot dwell upon these differences as we descend in 
the scale of animal life without entering too minutely into 
the subject of Comparative Anatomy. 

The Periosteum. — The surfaces of bones are covered 
bv a fibrous membrane, through which bloodvessels and 




Fig. 8. — Hip-joint.* 
1,2, 3, ligaments. 



nerves pass for the nutrition of the bone, called the peri- 
osteum, strictly from its derivation from two Greek words, 
meaning " over or about the bone." 

The Joints. — A passing allusion has already been made 



* The bone in Fig. 8 is represented as unnaturally moved from its 
socket, so as to show the cavity. In Fig. 9 the ligaments of the elbow 
appear as if separated, for the same renson. 



THE BONES, JOINTS, AND MUSCLES. 



35 



to some of the modes in which bones are separated from 
one another. Strictly speaking, we might say that the 
bones are never thus separated absolutely, for they are 
attached to each other at every part of the body, although 
in very different ways. Some 
of the joints — or articulations 
as they are called — are mov- 
able; others are immovable. 
Those that are movable re- 
quire strong ligaments or 
bands to keep them suf- 
ficiently in their place to pre- 
vent dislocation. Ligaments 
are white fibrous cords, which 
yield so little when the bone 
moves in the joint that some- 
times when great force is ap- 
plied the bone will break and 
the ligament sustain no injury. 
When violently stretched or 
twisted, however, what is gen- 
erally called a "sprain" or 
"strain" results. In some 
articulations the surfaces are 
covered with a fibrous and 
elastic substance called car- 
tilage, which is able to resist 
the application of great force 
or shocks. This cartilage is bathed by a fluid called the 
syno'vial fluid, on account of its resembling white of egg, 
which allows the surfaces to move smoothly over one an- 
other. The machinery is thus lubricated, as it is familiarly 
called in the phraseology of the workshop when oil is 




Fig. 9. — Elboav- joint. 
1, bones of forearm.; 2, ligament 
3, bone of arm. 



36 



PHYSIOLOGY. 



applied to the joints and working-parts of the steam- 
engine. Strength and ease of motion are thus imparted to 
the joint by the ligaments, cartilages, and synovial fluid 
combined. The greatest freedom of motion is seen in the 
shoulder-joint, which is a familiar illustration of a ball- 
and-socket joint ; another example of which is seen in the 
hip-joint (Fig. 8). The elbow, knee, and wrist have a 
hinge-like movement familiar to all. The mode in which 
the different bones fit into one another, and the arrangement 
of the cartilages, cavities, etc., are well shown in Fig. 9. 

A The Muscles. — The erect 

position of the body is main- 
tained chiefly by the action 
of the muscles in connection 
with the bones. These are 
a series of organs, familiarly 
known as the flesh, which 
abound in every part of the 
body, giving it shape and 
directing its movements. The 
muscles are about four hun- 
dred in number. Meat, as it 
is familiarly called, is the 
muscular portion of the ani- 
mal body which is used for 
food. 

Muscular Fibres. — When a 
muscle is examined under the 
microscope it is found to be 
made up of a large number of small fibres, or fibrils* as 




Fig. 10. — Fibrils of Muscle. 
A, B, muscular fibrils; A', cross- 
section of one of the discs com- 
posing them. 



*The general arrangement of the fibrils when deprived of the mem- 
brane covering them is seen in Fig. 10, A, one of the rings composing it 
being here represented, still further enlarged. 



THE BONES, JOINTS, AND MUSCLES. 



37 



they are called, too minute to be seen by the naked eye, 
and parallel to one another. These fibrils (Fig. 10, B) are 
the contractile portions of the muscle. A large number 
of them are united into bundles, which are placed parallel 
with other bundles, from which they are separated by a 




Figs. 11, 12.— Actions op a Muscle illustrated. 



loose tissue called areolar or cellular tissue. These bundles 
combine with other bundles, and so on. The muscles are 
usually placed between or in contact with bones, sometimes 
by both extremities of the muscle, or, as in the case of the 
eye, by one end only. The action of muscles, wherever 
they exist, is motion, in some form. Sometimes the motion 
is voluntary ; at other times, as in the heart, which is a 

4 



38 



PHYSIOLOGY. 



muscular organ, it is involuntary, or beyond the control 
of the will. As a general rule, the voluntary muscles are 
striped by parallel lines, and hence the term striped or 
striated muscles applied to them. The heart is an excep- 
tion, being striped and yet involuntary. All muscular 
movement that occurs during sleep is carried on by invol- 
untary action of the muscles. Those which are concerned 
in breathing, by raising and depress- 
ing the ribs or moving the muscles 
of the abdomen, are partly voluntary 
and partly involuntary, so far as the 
nervous system controlling them is 
concerned. 

Tendons. — One of the best .ex- 
amples in the human body of a 
muscle producing voluntary motion 
is that generally known as the biceps 
of the arm, so called because it has two 
heads or origins (Fig. 12, a, a). The 
effect of its contraction is shown to be 
the bending of the forearm at the el- 
bow in a direction toward the shoulder. 
The natural appearance of the muscle 
when in a state of repose is also exhibited. The fibres of 
muscles terminate (as seen in Fig. 12, b) in a fibrous non- 
contractile tissue, to which the name tendon has been 
applied. By this tendon it is firmly inserted into the 
bone, and all direct action of the muscle on the bone in 
moving the limb is exerted through it. Some of the 
tendons just beneath the surface of the skin can be felt at 
different points, such as the back part of the knee and at 
the elbow. The most powerful tendon in the body is that 
which is inserted into the heel, and is controlled by the 




Fig. 13. — Tenik> Achil- 
les. 



THE BONES, JOINTS, AND MUSCLES. 



39 



muscular mass oh the back of the leg (Fig. 13). It is 
known as the tendo Achilles, from the fact that this was, 
in mythological story, the only vulnerable part of the body 
of Achilles. Another fibrous 
arrangement connected with the 
muscles is called an aponeurosis 
(because it resembles nervous 
tissue, according to the notion 
of the ancients). It is a white, 
shining membrane, very resist- 
ing, and differing only from the 
tendons in its flat form. It is 
sometimes continuous with the 
muscular fibres, and at other 
times forms a covering for them, 
surrounding them so as to pre- 
vent their displacement. In the 
extremities it not only invests 
the whole limb, but gives off 
portions to pass in between the 
various muscles (Fig. 14). 

Contracti I ity. — The character- 
istic property of the muscles is 
their power of contraction, or 
contractility, as it is called. The 
result of this contraction is to 
diminish the muscle in length, 
while at the same time it becomes broader or swollen 
from side to side. The shape of the muscle as a fleshy 
mass therefore becomes considerably changed (Fig. 11). 
The hardness which is felt when the hand is placed over 
the muscles of the arm when the forearm is flexed or bent 
at an angle to the arm is caused by the forcible tension of 




Fig. 14. — Aponeurosis of the 
Leg. 



40 PHYSIOLOGY. 

the muscular fibres produced by their contraction. The 
changes, therefore, which a muscle undergoes in contracting 
are a shortening of its length, an enlargement in its thick- 
ness, and a greater degree of firmness and tension. After 
contraction, which lasts for only a short time, and results 
in fatigue if long continued, the muscle returns to its pre- 
vious condition of repose. The parts on which it had 
acted while in a state of contraction also resume the 
position they had assumed when influenced by that muscle 
or series of muscles, or assume some new position ; but 
this effect is not produced by the muscles which had 
already acted upon them, but by another set, which, from 
their acting in opposition to them, are said to be antago- 
nistic muscles. 

Muscles that bend the joints are called flexors, and 
those which restore the part to its straight condition are 
called extensors, and these two sets of muscles are excellent 
illustrations of the antagonism already referred to. The 
muscles of the arm and the leg which bend or straighten 
those parts are flexors and extensors respectively. Although 
called antagonists, they do not oppose each other or coun- 
teract their individual movements while either set is on 
duty ; each muscle or set of muscles — whether flexor or 
extensor — waits until its opponent has performed the work 
assigned to it. Should both sets of muscles be called into 
play at once, the result would be complete rigidity and 
absence of motion in the limb. Fatigue soon results, 
however, from such a forced condition of the muscular 
apparatus. Rest is absolutely necessary for the muscles, 
even those which, being beyond the control of the indi- 
vidual, have been called the involuntary muscles. The 
heart, for example, which is supposed by many to be 
always at work and never to rest, has really a brief period 



THE BONES, JOINTS, AND MUSCLES. 41 

of repose between its pulsations or beats. Muscles require 
such a rest to enable them to recover from their fatigue and 
to acquire new strength. The fatigue of keeping a limb, 
such as the arm or the leg, in an outstretched position for 
any length of time is a familiar illustration in point, 
whereas if the part was properly, exercised the alternate 
contraction and relaxation would preserve the tone and 
viffor of the muscle. 

Movements. — The movements of the body in walking, 
running, leaping, etc. are examples of the influence and 
utility of the muscles. 

Walking is apparently a simple matter of e very-day 
experience, but it is a series of complicated movements of 
the flexor and extensor muscles of the legs. It is motion 
on a fixed surface, the centre of gravity of the body being 
moved alternately by one of the extremities and supported 
by the other without absolutely leaving the ground. In 
walking the limb is directed forward, and the weight of 
the trunk is supported by the hip-joint — that is to say, by 
the head of the thigh-bone. This weight is transmitted 
to the ground by the principal bone of the leg and by the 
bones of the foot. Then the opposite lower limb advances 
in its turn, and supports alone the weight of the body, 
while the limb that is behind is in repose. For a single 
moment, but a very short one, in these successive steps, the 
body rests upon both legs at once. The essential point in 
the process of walking is the fact that the heads of the 
thigh-bones form fixed points, on which the pelvis turns 
alternately as upon a pivot, describing arcs of circles, which 
are greater in proportion to the size of the steps. 

In running, the foot that remained behind is detached 
from the ground before the other reaches it, and there is 
not a single instant in which the body rests upon both feet 

4* 



42 PHYSIOLOGY. 

at once. At some moments, indeed, both feet are entirely 
raised from the ground. Running is really a succession 
of low leaps performed by each leg alternately. It differs 
from walking in the fact that the body is projected for- 
ward at each step, and the hindmost foot is raised before 
the foremost foot touches the ground. In running, the 
body is inclined forward, so that the centre of gravity 
may be properly placed to receive an impulse in that 
direction from the hindmost leg; and the foremost leg is 
advanced quickly to keep the vertical line within the base 
of support, and thus prevent the body from falling. 

In leaping, the whole body is raised from the ground, 
and the limbs are suddenly extended after violent flexion. 
Swimming resembles leaping, but there is no fixed surface 
from which the muscular effort is made. Many other mus- 
cular movements are possible, such as are called into play 
in climbing, carrying a load, etc., but it is not necessary to 
enter more fully into an explanation of them. 

Effect of Exercise. — As the bones give general outline to 
the body, so do the muscles fill up all the details, giving 
the individual his characteristic features, shape, etc. The 
development of the muscular system is dependent upon the 
amount of exercise to which it is subjected. We therefore 
find such occupations as call the muscles into active play 
producing in them greatly increased development ; the 
blacksmith, for example, having the muscles of his arm, 
especially the biceps above referred to, largely increased 
in size and power. The amount of development, therefore, 
varies also with the age and with the sex, being generally 
slight in children and in females. All development, how- 
ever, must be gradual, and not forced or violent. All the 
attitudes practised in gymnastics are intended to have the 
effect of strengthening the muscles of the arms and legs 






THE BONES, JOINTS, AND MUSCLES. 



43 



and chest, but great care must be taken not to exceed mod- 
eration in the exercise, as the muscles may be developed at 
the expense of the powers of the individual. A familiar 
effect of the gradual exercise of the muscles under proper 
training is seen in the preparation of horses for racing. 
They are brought very slowly into proper condition, and 
at first they exercise without any weight upon their backs, 
and afterward, but gradually, with a weight that is increased 
by degrees up to the proper standard. 

During waking hours all the muscles are never in repose 
at one time. While standing the extensor muscles of the 
limbs and the muscles which support the head and spine 
are in a state of tension. When we sit down without 
having any support to the back, the muscles which sup- 
port the spinal column and the head must be in a state of 
tension, and if the back be supported, then the muscles 
of the head must be in a like condition. During sleep the 
power of the will over the muscles is subdued and the 
muscles become relaxed, and each part falls or drops, as 
the head upon the chest, according to the laws of gravity. 
It is easy to understand why a person becomes easily fatigued 
from such continuous tension. Repose or rest of the mus- 
cles concerned is absolutely necessary. 

Names of Muscles.— All the muscles of the body have 
received names, but these are important only to the anat- 
omist, one who makes a special study of all the different 
minute parts of the body. We need only know them in 
classes by the work they have to do. We have already 
spoken of flexors and extensors; the flexor muscles of the 
leg, for example, passing from the back of the thigh to the 
back of the leg, and the extensor muscles from the front of 
the thigh to the front of the leg. Then we have muscles 
which draw the arm or the leg away from the body, and 



44 PHYSIOLOGY. 

these are called abductors, and others which move them 
toward the body, and these are called adductors. If a 
part is lowered by a muscle, the latter is called a depressor ; 
if it compresses a part, it is called a compressor; if it 
dilates, a dilator. It has been already shown in illustrat- 
ing the bones that they are arranged in pairs (Fig. 1) ; that 
is, that both sides of the body, the right and left, have, as 
a general rule, the same bones on both sides of a median 
line. The same remark is true of the muscles, which are 
alike on both sides of the body, except when the muscle is 
single and divided into two parts by the line drawn through 
the middle of the body. 

Muscles of Expression. — Besides giving motion to the 
limbs and bones in various parts, the muscles have other 
important duties to perform. The bones of the face, for 
instance, are not at all movable upon one another, except 
in the case of the lower jaw, yet the whole expression of 
the face in its various emotions, as joy, anger, grief, etc., is 
dependent upon the play of the muscles connected with the 
soft parts of that region (Fig. 15). In some parts of the 
body a great deal of work is performed by the contraction 
of muscular fibres that are almost, if not wholly, micro- 
scopic, as in the smaller air-tubes, in which the action of 
the muscles assists in the process of breathing. In the face, 
the muscles connected with the eyelids, nose, eyebrows, lips, 
cheeks, tongue, etc. all assist in the expression of the emo- 
tions, and combined they give to each individual his identity 
and peculiar features. The motions of the face and neck 
are controlled by about seventy pairs of muscles in different 
layers. 

When muscles are allowed to remain unused for any 
length of time they lose their firmness and are lessened in 
size, becoming softened and weakened in power. Seden- 



THE BONES, JOINTS, AND MUSCLES. 



45 



fcary occupations and indolence have the same effect, and 
the whole system sympathizes, so that the general health 
suffers. Exercise in the open air is absolutely necessary 
each day, and should not be crowded into one day, to the 




Fig. 15. — Muscles of the Face and Neck. 

exclusion of that proper to the rest of the week. This 
over-exerCise must be avoided under all circumstances. 
The modes of exercise must be left to each individual 
judgment and choice. Walking, in moderation, is perhaps 
the most convenient form, although riding calls additional 
muscles into play, and stimulates the nervous system by the 
peculiar open-air exercise attendant upon it. There should 



46 PHYSIOLOGY. 

be but little if any fatigue after exercise, whatever its form 
may be. Some of the games in which children indulge to 
excess should therefore be practised with moderation, such 
as jumping rope, etc. It seems to be a delusion with 
many persons that the young can accomplish without 
injury feats of agility which those older in years would 
shrink from. Exercise in the open air is, however, strongly 
to be commended, but each one must learn what is his own 
capacity, and not exceed it. The object should be to pro- 
mote the general health and develop all parts of the system 
in accordance with such a result, and not any part of it to 
excess at the expense of other parts or without regard to 
the improvement of the whole system. 



QU ESTIO NS 



What useful purposes do the bones serve ? 

What organs are protected by them from injury in the skull? In the 
chest? In the spinal column? 

What organs are directly concerned in the movements of the body? 

Of what two parts are bones composed ? What is the effect of each? 

What is the condition of bone when being first formed? 

What useful purposes does cartilage serve? 

How are the bones of the skull adjusted? 

Is any one of the skull-hones movable? 

How are bones divided ? 

What is the interior structure of a long bone? 

What is the effect of such an arrangement? 

What is the appearance of the solid portion under the microscope? 

What use have these canals? 

What is the technical name of the back-bone? 

What is its general arrangement ? 

How many bones compose it? 

In what is the spinal cord contained? 

What is the arrangement of elastic tissue in the spine, and what are 
its uses? 



THE BONKS, JOINTS, AND MUSCLES. 47 

How can this be illustrated by experiment? 

To what bones is the spinal column attached above and below ? 

What familiar nautical illustration is offered? 

How does the head move on the spinal column? 

What are the two upper bones of the spinal column called ? 

What is the thorax, and with what function is it particularly con- 
cerned ? 

How many bones compose the upper limbs? The lower limbs ? 

How are the bones all attached to one another ? 

What peculiarities in the limbs are found in the lower classes of 
animals? 

What is the membrane covering bones called? What are its uses? 

How are bones connected together ? 

What kinds of joints or articulations do we find ? 

What are ligaments? 

What is a sprain ? 

With what material are joints sometimes strengthened ? 

What fluid is found in the joints? What are its uses? 

flow do the various joints, as of the elbow, shoulder, hip, etc., differ 
from one another ? 

What organs preserve the erect position of the body ? 

What is flesh? Meat? 

What is the appearance of muscles under the microscope? 

W T hat kind of tissue separates the fibres ? 

W T hat is the action of muscles wherever found ? 

Is this motion under the control of the will? 

What is the arrangement of the fibres in voluntary muscles ? 

What great organ is an exception to this ? 

What is the arrangement of the biceps muscle, and how does it con- 
nect with the bone ? 

What is a tendon ? What is the most powerful tendon in the body ? 

What is an aponeurosis? 

What is the result of contraction of a muscle? 

What takes place when this contraction ceases? 

What are antagonistic muscles? 

What are flexors and extensors? 

What is the effect of their separate action? Of their combined 
action ? 

What rest does the heart have from labor? 

What rest do the muscles as a class have during their work? 

What is the general muscular action involved in walking? 



48 PHYSIOLOGY. 

What is the essential point so far as the hip is concerned in this 
process ? 

What occurs during running? 

What is the muscular movement in leaping? In swimming? 

What effect has exercise, such as occupation, on muscles? 

What effect have age and sex on their development? 

Wiiat is the effect of gymnastics? 

How is this exemplified in the training of horses? 

How are the muscles affected in standing, sitting, etc. ? During sleep? 

What are flexor muscles ? Extensor muscles? Abductors? Adduc- 
tors ? Depressors ? 

How are the muscles arranged in pairs? 

What peculiar action have the muscles of the face ? 

What duty is performed by microscopic muscular fibres? 

W T hat muscles of the face assist in giving expression? 

How many muscles control the motions of the face and neck? 

What is the effect of the non-use of muscles? 

What rules should be observed as to exercise? 

What modes of exercise are commended? 

What is the object of exercise ? 



DIGESTION. 



Digestion is the process by which food becomes con- 
verted to the needs of the system. The changes which it 
undergoes occur mainly in the stomach and intestines. 
When taken into the mouth it is not in a fit condition to 
be absorbed, and therefore requires, at various portions of 
the digestive apparatus, such action upon it as will adapt 
it to the nourishment of the animal. The system is con- 
stantly undergoing a process of wear and decay, and diges- 
tion is the most important means of supplying materials 
for the restoration of life and vigor by the repair of such 
losses. When food is taken into the mouth, all the nutri- 
tious portions are separated from it as it passes through 
the different parts of the digestive apparatus. In other 
words, Digestion fits it to be absorbed, while Absorption, 
which we shall afterward describe, carries it into the cur- 
rent of the blood, through which fluid the body is directly 
nourished. 

Digestion in the Vegetable. — Digestion takes place in the 
vegetable as well as the animal. It is of a very simple 
nature in the former. The soil supplies the materials, 
which are mainly water, carbonic acid, ammonia, etc., de- 
rived from the surrounding atmosphere. These are con- 
densed in a porous soil and placed within the grasp — if we 
may so call it — of the plant, the rootlets of which become 
thoroughly mixed with the soil as they penetrate it in all 

5 D 49 



50 PHYSIOLOGY. 

directions. The greater part of the carbon in the vege- 
table is derived from the soil in this way. Sometimes 
chemical substances, such as gypsum, which is a prepara- 
tion of lime, are added to make the soil more porous, and 
thus increase its powers of condensation ; charcoal acts in 
the same way. The various substances necessary for the 
nourishment of the vegetable come in contact with the 
expanded extremities of the rootlets ; and under the influ- 
ence of absorption, in the form of imbibition, as this is 
technically called, fresh portions are continually passing up 
to the stalk, forming the sap, which goes to the nutrition 
of the plant. 

Food of Man. — As a rule, the articles employed for food 
are derived from the animal and vegetable kingdoms. By 
the term food, or aliment, we denote such solid substances 
as are capable of being converted into chyle (a name given 
to the digested mass after it has been subjected to the ac- 
tion of the alimentary canal ), and such liquid substances as 
can be readily absorbed for the wants of the system. In 
some parts of the world, however, mineral substances, such 
as earth, are occasionally eaten alone or mixed with bread, 
but no nutriment is derived from such articles. They fill 
the stomach and satisfy its demands for the time being, but 
have no other effect. In countries where grain and fruit 
are abundant the inhabitants naturally adopt that form of 
diet, while in other regions, with little vegetation, they live 
almost entirely on animal food. 

As already stated, the taking of food supplies materials 
to make up for the losses which the body necessarily sus- 
tains as a part of its existence. In early life the body gains 
in this way more than it loses, and hence it grows. After 
a while the amount lost and gained becomes about equal, 
and the body gains or loses but little in weight. Sometimes 



DIGESTION. 51 

in old age the body loses more than it gains, and the weight 
decreases. 

To ensure perfect health the same ingredients should be 
taken in the food that are necessary to the composition of 
the body. The substances usually employed as articles of 
diet, such as meat, milk, water, and vegetables, contain a 
variety of elements fully adapted to the wants of the sys- 
tem. Milk alone contains a sufficient number of these to 
form the sole diet of the young child, and indeed of the 
young of other animals. 

Milk and flour are strikingly like the blood in their com- 
position, and are therefore well adapted as articles of food 
for the repair of the body. This may be shown at a glance 
in the following table : 



Flour. Milk. Blood. 



Fibrin, 



f Fibrin. 

AJbumen, }■ ..Curd or Casein.. -J Albun,en - 

^ • I Casein. 

Casein, J \ . 

[ Coloring-matter. 

Oil Butter Fat. 

Sugar, starch Sugar Sugar. 

Inorganic substances, Inorganic sub- Inorganic sub- 

such as preparations stances, etc. stances, etc. 

of soda, potassa, lime, 
iron, etc. 

It will be seen that flour, milk, and blood all have sugar 
and fatty matter and chemical and albuminous substances 
in common. 

Water, which is so necessary as part of our nourishment, 
contains a certain amount of mineral matter, and every 
portion of the body requires that mineral matter be present 
in its solids and fluids. Indeed, the animal begins to fall 
off in its nutrition when deprived of these materials. 

Condiments. — Common salt is found in every part of the 



52 PHYSIOLOGY. 

body, and man and animals generally instinctively recognize 
its necessity as an article of diet. When taken by man as 
an aid to digestion it is called a con'diment, a name under 
which are embraced pepper, mustard, and other such aux- 
iliary articles. It has been thought by some that salt has 
the power of assisting the activity with which certain arti- 
cles of diet are absorbed during the process of digestion. 
Lime, which exists in the bones and teeth, and minutely 
in other tissues and fluids, is taken into the system, often 
without our knowledge, as an ingredient of water and other 
articles ; and the same may be said of other substances. 
Soda, potassa, and magnesia are also found in different por- 
tions of the body. In studying the circulation of the blood 
we shall find that iron exists in the coloring-matter of that 
fluid. AVhen this material is deficient in quantity the 
individual acquires a peculiar paleness, and the general 
nutrition of the body suffers. The natural color returns 
under the use of iron as a medicine. The amount of iron 
in the body has been estimated at about forty-five grains. 

Ingredients of Food. — A number of articles employed as 
food contain as their chief constituents the two elements, 
carbon and hydrogen. These are starch, gums, mucilag- 
inous materials, cane-sugar, and grape-sugar. Starch is 
eaten in the form of potatoes, arrow-root, rice, corn, beans, 
etc. Carrots, melons, turnips, cucumbers, etc. furnish cane- 
sugar, which is also derived from the sugar-cane or beet- 
root. Fruits, honey, etc., and wine, beer, cider, etc. — fer- 
mented liquids — contain grape-sugar. In some of the mus- 
cles, as of the heart, a similar sugar is found to exist, and 
a kind of starch formed in the liver becomes converted also 
into grape-sugar. Fats are usually taken as food in the 
solid form, as butter or lard, or in the liquid, as oils, such 
as olive oil. A classification of aliments has been made, 



DIGESTION. 53 

called the nitrogenized, because they contain nitrogen. 
They are also called albuminous substances, because they 
contain albu'men, or matter resembling white of egg. 
These are usually derived from animals, being con- 
tained in the muscular parts of flesh, in the milk, in the 
white of eggs, and the gelatinous principles obtained in 
soups from the skin, bones, etc. of animals. Vegetables 
also supply them from the gluten or nutritious part of 
grain and seeds, of peas, beans, etc. 

In addition to these essential articles, others are taken, 
according to individual caprice or fancy, such as condi- 
ments, already alluded to ; alcohol in the form of wines, 
beer, spirits, etc. ; tea, coffee, chocolate, etc. Some of these, 
as alcoholic drinks, may aid the digestive process when 
taken in small doses, but they are not essential, and may 
frequently be positively injurious. Acid drinks, claret, 
lemonade, etc., temporarily relieve thirst and stimulate the 
secretion of saliva and of the juices of the stomach when 
taken in small quantities, and pepper and mustard as con- 
diments have a similar effect, but healthy digestion can go 
on perfectly well without them. 

Classification of Food. — Some authorities have divided 
all food into two classes: those which contain nitrogen 
are called niirogemzed, and those which do not, the non- 
nUrogenized ; the former predominating in animals, the 
latter in vegetables. A due admixture of both is necessary 
to perfect health. Nitrogen forms an essential constituent 
of the animal tissues ; hence its importance as an article of 
diet. It has been shown that animals and vegetables con- 
tain both classes of food, so that animals which live en- 
tirely upon flesh could be nourished for a while on veg- 
etable food, and vice versa. As there is less nitrogen in 
vegetable food, an animal living entirely upon it is com- 



54 PHYSIOLOGY. 

pel led to eat a larger quantity in the course of a day than 
one which eats meat entirely. It is said that a dog will 
thrive if it takes one-thirtieth of its weight in animal food, 
while a horse consumes a tenth or twelfth of its weight in 
vegetable food. Animals that are restricted to one class 
alone soon fail in health and die, while they would live if 
confined to a single article, as milk, which contains both 
nitrogenized and non-nitrogenized elements. Variety of 
food is, however, essential to healthy digestion in all ani- 
mals which are accustomed to a mixed diet. A disease 
called scurvy may result in man when such variety is im- 
possible, as in some of the voyages of discovery to the 
Arctic regions ; although here it was found, in more than 
one instance, that a change to another article of the same 
class relieved for a time this condition. All diet-tables for 
the army and navy, for the use of officers and men for the 
preservation of their health, are made up of a due admix- 
ture of both kinds of food. 

Some of the more important ingredients of food, such as 
oils, fats, starch, sugar, etc., deserve brief mention. 

Oils and Fats. — Animals and vegetables — such as the olive 
and the palm — supply oily matter of different kinds. This 
is generally found to consist of three chemical substances, 
called oleine, stearine, and margarine. These three sub- 
stances are compounds of glycerine, which is the sweet 
principle of fats, in combination with a fatty acid. An 
oily substance is soft or firm according to the proportion 
of these contained in it ; it is called a fat if it is of firm 
consistence, and an oil if it is more fluid. When examined 
under a microscope, each drop of oily matter appears in 
round globules of different sizes, and the crystals of fat 
are seen mixed with them. Oils are not soluble in water, 
but they mingle with it in a mixture called an emulsion, 



DIGESTION. 55 

which is only a mode of holding oily matter in a state of 
fine division. Milk itself is an example of an emulsion, 
for under the microscope we find numerous oil-globules in 
it, and we obtain butter from it. Oily matters are largely 
taken as articles of food in regions of extreme cold, such 
as the Arctic regions, where it becomes necessary to keep 
up the temperature of the body by such diet. Tallow can- 
dles and the coarsest oils are eaten in large quantities by 
the people of those latitudes. 

Sugar. — This is derived from a variety of sources, such 
as the sugar-cane, sugar-maple, and beet-root. It is present 
in the vegetable during inflorescence or flowering, and is 
the characteristic ingredient of sweet fruits, where it exists 
in combination with vegetable jelly. The bee collects it 
from various flowers in the shape of honey. Sugar is a 
very nutritious article of diet. It is soluble in water, fer- 
ments very easily, and is very digestible. Cane-sugar is 
the form usually employed, but in fruits another variety 
exists, called grape-sugar, which is not so sweet or so 
soluble. 

Starch. — This element of food is very extensively diffused 
through the vegetable world. In rice, barley, etc. it is in 
an almost pure state, but it is mixed with sugar in some 
grains, as oats, and in seeds, such as beans, peas, chestnuts, 
potatoes; with mucilage in oily seeds, like the almond, 
hempseed, hazelnut, etc. Starch is prepared artificially 
from various substances, as wheat, corn, and the potato. 
From a hundredweight of potatoes we can get about 
fifteen pounds of starch. The different flours are largely 
starch. Starch does not dissolve in cold water, and is not, 
therefore, digestible in that shape, but under the action of 
boiling water the grains of starch discharge their contents 
and undergo solution. 



56 PHYSIOLOGY. 

Gum. — This is also found in vegetables, and is often used 
as an article of diet. During the gum-harvest season in 
some parts of Africa the natives are said to live entirely on 
it, taking about half a pound a day each. It is not consid- 
ered, however, as specially nutritious, and is not very digest- 
ible. Gum arabic is one of the best-known articles of this 
class, and is itself the juice obtained from making incisions 
in a tree, particularly in the part of the world which has 
given it its name. 

Albuminous Substances. — These are the most important 
of all the articles employed as food, without which life 
cannot be sustained. The nutritive principles of this class 
are called albumen, fibrin, and casein. Albu'men exists in 
its purest state in the white of egg, which gives it its 
name (albus, white). It is found in meat and milk and in 
most of the animal solids, and is present in considerable 
quantity in all the fluids which are concerned in the nutri- 
tion of the animal. The egg of the bird contains hardly any 
other ingredient except the albumen, if Ave except the 
yellow fatty matter of the yolk, and yet the whole chicken 
is developed from it, including feathers, claws, bloodvessels, 
and everything else that forms part of the animal. Fi'brin 
is found in the body in a fluid state in the blood and in the 
lymph and chyle — fluids which will be studied hereafter — 
and in the muscles. In many of the cereals, as they are 
called, or vegetable grains — in wheat especially — a highly 
nutritious substance is found, which is called glu'ten. It is 
obtained from wheaten flour by kneading under a stream 
of water. We see a good example of gluten in bread, 
which owes its peculiar porous character and consistence 
to that substance. Gluten contains vegetable fibrin and 
albumen, which resemble animal albumen and fibrin. 
Ca'sein is the principal ingredient in the milk, of the upper 



DIGESTION. 57 

classes of animals especially, and is the envelope which 
surrounds the oil-globules or butter-globules floating in 
that fluid. What is called curds and whey is nothing 
more than the casein of milk coagulated with rennet, the 
rennet itself being an infusion of the mucous or lining 
membrane of the fourth stomach of the calf. 

The albuminous substances are all rich in nitrogen, but 
to ensure perfect digestion it is necessary to combine with 
them a proper mixture of fatty principles or substances 
containing mineral matters, such as common salt, etc. Such 
a mixture is adopted almost as a matter of course ; for ex- 
ample, bread and butter, potatoes and beef, or milk alone,, 
which is itself a mixture of both albuminous and fatty 
matters with sugar, etc. 

The following table exhibits the amount of starch, sugar, 
albumen, Avater, etc. in the various articles of food in 100 
parts of each : 





Water. 


Albumen. 


Starch. 


Sugar. 


Fats. 


Salts. 


Bread 


37 


8.1 


47.4 


3.6 


1.6 


2.3 


Wheat flour 


15 


10.8 
12.6 


66.3 

58.4 


4.2 
5.4 


2. 
5.6 


1.7 


Oatmeal 


15 


3. 


Rice 


13 


6.3 


79.1 


0.4 


0.7 


0.5 


Potatoes 


75 


2.1 


18.8 


3.2 


0.2 


0.7 


Peas 


15 


23. 


55.4 


2. 


2.1 


2.5 


Milk 


^6 


4.1 




5.2 


3.9 


0.8 


Cream 


06 


2.7 




2.8 


26.7 


1.8 


Cheese 


36.6 


33.5 






24.3 


5.4 


Beef. 


51 


14.8 






29.8 


4.4 


Pork 


39 


9.8 






48.9 


2.3 


Poultry 


74 


21. 






3.8 


1.2 


Whitefish 


78 


18.1 






2.9 


1. 


Egg 


74 


14. 







10.5 


.1.5 



The study of such a table enables us to know what arti- 
cles of diet should be taken together. Those that have plenty 
of albumen, for instance, should be combined with others 
that are largely starchy, in order to ensure a full diet. 



58 PHYSIOLOGY. 

Gelatin. — When the organic parts of bones, skin, ten- 
dons, etc. of animals are boiled for a length of time, they 
are converted into a substance called gel'atin, which is 
soluble in hot water, but cools into a jelly-like mass. Ex- 
periments have been made to determine whether it has any 
nutritious effect when given as an article of diet. It was 
said that when animals were restricted to this exclusively 
they fell off in their nutrition, and were compelled to have 
other kinds of food given to them as well. It has been 
found, however, that such might be the case if an animal 
were restricted to any one kind of food, whether it be 
gelatin or any other article. 

AVe have thus seen that the important classes of articles 
used as food belong, as a rule, to the three great divisions 
of albuminous, oily or fatty, and sugars or starches, for 
the latter are convertible into sugar. 

Animal and Vegetable Food. — If we consider the two 
great classes of animal food and vegetable food, we find 
much to interest us. 

Animal Fond. — Almost every part of animals has been 
used as aliment, but the portion universally emploved is 
the flesh, by which we mean the muscles of voluntary 
motion. The use of blood as food was forbidden among 
the Hebrews — not from any injurious effect it might be 
supposed to possess, but because it was thought that they 
might by familiarity with it feel less horror at shedding 
the blood of their i'el low-creatures. Attention has of late 
years been attracted to the presence of a minute animal — a 
worm, called the trich'ina spiralis (which two words only 
mean a "spiral, hair-like animal") — in the various forms 
of pork, as ham, sausages, etc., especially when not thor- 
oughly cooked. This worm may thus get a foothold in the 
human system and produce a serious and painful disease. 



DIGESTION. 59 

The character of animal food differs according to its 
age, the material it has fed upon, on climate, season, fat- 
ness, etc. An extremely young animal's flesh has more 
gelatin in it and is more soluble, but not always on that 
account more digestible. Calves' meat — veal — is not as 
digestible, for example, as beef. The fat of the young 
animal is arranged around the muscles, while in the older 
it lies more between the fibres of which the flesh is com- 
posed, giving it a marbled appearance. So far as the season 
is concerned, the flesh of animals is in better condition 
during the early winter months after an abundant feeding 
during summer ; in the spring the flesh is lean from de- 
ficiency of nourishment. Fat animals are more desirable 
for food, because the admixture of fat and lean makes the 
flesh more soluble. The lean of fat meat is therefore to 
be preferred on account of its being nutritious and digest- 
ible, although the fat itself is less digestible than the flesh. 
Meat is really more digestible, although decidedly less 
palatable, when kept until it begins to spoil ; but game is 
the only kind of flesh that ever finds favor in this respect. 
Venison is often eaten in this condition, but the taste has 
to be educated to it. The breath is not affected by such 
food, for the secretions of the stomach have the power of 
immediately destroying the disagreeable odor of putrid 
substances. The tenderness of the meat under these cir- 
cumstances is caused by the destruction of the cohesion 
between its particles when it begins to be decomposed. 

All parts of birds, as well as the eggs of many of them, 
have been taken as human food. Those parts which are 
continuously exercised are not as tender ; hence a chicken's 
wings are more delicate than the legs. A duck's legs, 
being less often used, are quite as tender as its wings. A 
woodcock's wing is more tough than that of the partridge, 



60 PHYSIOLOGY. 

because it flies more and walks less than the latter. Birds 
that chiefly live in the water, as the goose and duck, are 
not, as a rule, so digestible ; their fat is often rancid and 
fishy. 

The flesh of fish is much used as an article of diet. It 
consists mainly of fibrin, albumen, and gelatin. It is less 
nutritious than the meats usually employed, and more so 
than a purely vegetable diet. An oily fish, such as the 
eel, is less nutritious, as the oily matter is not so easily 
digested in the stomach. Tribes are found in various 
parts of the world who live on fish alone, that being the 
food which they can easily secure, after floods or heavy 
rains, with least trouble and expense. Such are said to 
be ichthyoph'agous — a sonorous word, .meaning, from its 
Greek derivation, "eaters of fish." Nearly every part of 
the fish is considered nutritious. A fish diet has been 
recommended by some as appropriate in cases of mental 
exhaustion and other forms of brain disturbance, because 
of the phosphorus contained in such food, the brain being 
largely supplied with that stimulating chemical substance, 
and being supposed to receive a fresh supply when this 
kind of food is taken. 

Milk. — As already stated, milk is well adapted from its 
composition to sustain life, being composed of such albu- 
minous, fatty, and saccharine matters in water as are well 
calculated for the nourishment of the body. When taken 
into the stomach it is doubtless converted by the fluids of 
that organ into a solid curd and a fluid or whey. The curd 
is digested just as any other substance would be digested 
there, while the fluid portion is absorbed into the blood- 
vessels, and soon becomes a part of the blood itself, going 
to the nourishment of all the living organs. Its nutritive 
properties adapt it to both sick and well. The cheesy part 



DIGESTION. (J 1 

of the milk sometimes disagrees from its not being digest- 
ible, and the curd formed in the stomach may remain there 
for hours. Generally milk agrees better than any other 
kind of food. Boiling makes milk much more digestible, 
especially if a little lime-water be added to it should it 
produce an acid state of the stomach. 

Derived from milk are cream, butter, cheese, buttermilk, 
and whey. Cream, carefully skimmed from the milk, con- 
tains casein and whey, together with the butter. Its oily 
nature renders it less digestible, but it does not turn acid 
as easily as milk. Butter, which is the oily part of milk, 
obtained by churning, is nutritious, but, like other oils, not 
very digestible. Cheese, which is the curd of milk, pressed 
and partially dried, carrying with it a. little butter envel- 
oped in it, is very nutritious, although not very digestible. 
It is considered by some in the light of a condiment, for, 
according to an old proverb, 

" Cheese is a surly elf, 
Digesting all things but itself." 

Cottage-cheese, or smeer-case — the soft curd of milk — is 
more easily digested. Buttermilk is the fluid left in the 
churn after the removal of the butter. When prepared 
from milk that has only been kept a little while, it may be 
perfectly sweet when first obtained. Having really lost the 
greater part of its fatty matter by the churning process, it 
should be more digestible, though not so nutritious. Whey 
contains a little sugar, cheese, and butter, which render it 
slightly nutritive, but it is apt to turn acid in the stomach. 
In Tartary, especially, the people use largely a beverage 
which they call koumyss, a kind of sour buttermilk, pre- 
pared from milk that has been allowed to stand for some 
days in a leathern churn until it becomes sour, when it is 
bottled for use. 

6 



62 PHYSIOLOGY. 

Eggs. — These have already been alluded to in referring 
to albumen. They are more nutritious than milk, but less 
digestible, no matter how they may be prepared. The white 
of the egg is almost wholly albumen in a pure state ; the 
yolk is oily matter with some albumen. Like albumen 
generally, the white of the egg coagulates by heat. It is 
more digestible when slightly boiled than when raw. The 
yolk, on account of its fatty matter, is not so digestible as 
the white. One great advantage of the egg as an article 
of diet is the large amount of nutritive matter contained 
in a small space. Fried eggs are less digestible, for the 
albumen becomes hardened and the oily matter is altered 
in its nature by the heat, so as to be unfitted for digestion. 
It may be stated, while referring to eggs as articles of 
diet, that all substances that contain a large amount of 
nutritious matter in a small compass are not easily digested 
by the stomach. 

Vegetable Food. — In some portions of the 'world vege- 
table food is almost the exclusive diet, and there are many 
animals — those we shall hereafter describe as the herb- 
ivorous class — which live entirely on this kind of food. 
As the great difference between animals and vegetables, in 
their chemical constitution, is the presence of nitrogen in 
the former, the question naturally arises, How docs the flesh 
of the animal get the nitrogen of which it is composed 
if there is none in the food ? The air it breathes is largely 
made up of nitrogen, and this is doubtless the chief source 
of its supply, passing into the animal's lungs, and thence 
into its general system. 

Bread is usually made from the flour of wheat. It con- 
tains principally a saccharineor starchy matter and gluten, 
to which reference has already been made. When prepared 
with yeast as a ferment, or with old paste or leaven kept 



DIGESTION. 63 

for the purpose, it is said to be leavened, and unleavened 
when made without such an addition to it. The effect of 
a ferment is to produce a thorough change of character and 
decomposition of the whole mass in which it is placed, 
and such a result takes place in regard to the flour. We 
shall hereafter see that the presence of a ferment, called 
pep' sin, is necessary in stomachal digestion. Milk sours 
and becomes curdy if kept for a while in a warm place, 
for the casein in it becomes itself so much altered that it 
acts as a ferment for the whole mass, developing lactic 
acid, which coagulates it. So with the flour; the gluten in 
it, mixed thoroughly with the starch and water, produces 
what we call bread. Unfermented bread will, of course, 
be more acceptable to the stomach, as the bread prepared 
by the other process is often somewhat acid. Sweet cakes 
are apt to be much less digestible, for they are generally 
made up of sugar and eggs ; and the same objections hold 
good in regard to pastry. 

Breads are made also of other flours, as bran, rye, barley, 
etc., but they are not so digestible or nutritious as that pre- 
pared from wheat, and are apt to turn acid on the stomach. 
Rice and corn flour are also eaten as bread, and are both 
digestible and nutritious. When soup is taken as an article 
of diet, the addition to it of any kind of bread, preferably 
wheaten bread, gives the soup a digestive texture, and enables 
the gelatin in it to be much more readily digested. The 
difference of texture of bread when hot and fresh and 
spongy, and when stale, probably accounts for the latter 
being more digestible. 

Fruits. — By some these are considered as the most health- 
ful articles that can be taken into the stomach ; by others 
they are looked upon as a fertile source of stomach derange- 
ments. As a rule to be generally observed, fruits should 



64 PHYSIOLOGY. 

be eaten only when perfectly ripe, the seeds and skins, 
which are thoroughly indigestible, being carefully removed. 
Such fruits as the melon and canteloupe are the least digest- 
ible of all this class. Preserved fruits act on the digestive 
organs just as sugar itself does, although the combination 
of fruit with sugar is not so likely to disorder the stomach 
as either sugar or fruits alone. 

Cooking. — The value of food depends upon its digesti- 
bility and upon the amount of materials it contains adapted 
to the nourishment of the body. The manner of prepara- 
tion of the food in cooking is also an important considera- 
tion. Few articles of diet are ready at once to be taken 
into the stomach without some such process. Cooking 
imparts flavor, and thus excites the secretions of the mouth 
and stomach, and at the same time renders the article more 
digestible by the softening and division of its particles, 
mechanically or by the aid of heat, water, or condiments. 
By heat especially, as in the making of beef-tea, the nu- 
tritious parts are entirely separated. 

The methods of cooking, such as roasting, boiling, stew- 
ing, etc., differently affect the digestibility of food by modi- 
fying its flavor, the arrangement of its particles, etc. It is 
said that the internal temperature of cooked meat should 
never go beyond 160°, nor fall below 130°. 

In roasting the heat is applied directly to the substance, 
which is placed in front of the fire or in an oven. Animal 
food is affected by roasting as follows : the albumen is 
coagulated, the fibrin shrivelled up, the fatty matters 
melted, and some of the water driven off. The appearance 
of meat after roasting is too familiar to be described. Of 
course, after losing so much fat and water, the weight is 
greatly lessened, but what is left in the meat is full of nour- 
ishment, while the gravy is also rich in nutritive material.- 



DIGESTION. 65 

Broiling is a means of applying heat directly to the 
article of food by placing it before or over the fire, as on 
a gridiron. The effect is to brown the surface and to retain 
the juices of the meat, and this process is regarded as the 
best to preserve its tenderness. 

Boiling has the effect of softening the food, so that the 
stomach can more readily act upon it. Water or steam is 
the vehicle through which the heat is applied. The boil- 
ing water dissolves out some portions of the flesh that are 
retained by the other processes, and about eighty per cent, 
of the salty matters, and the heat coagulates the albumen, 
while the gelatin in the meat is converted into a jelly-like 
mass. If there be much albumen in it, boiling to excess will 
produce a hard, over-boiled mass ; while if there be much 
gelatin, as in young meat, a jelly-like substance results, 
which is quite as indigestible. Boiling produces a loss of 
weight, but not nearly so much as by roasting. In stewing 
a less amount of water is employed. 

Frying not only requires a pan in which the article is 
placed, but also the addition of some fatty matter. As oil 
or fat is thus exposed to heat, and mixed with the sub- 
stance, it is less digestible, and is very apt to disagree. 

When vegetables are cooked, some parts, as the gum and 
starch, are dissolved out ; if not soluble, they are softened, 
and thus better fitted for digestion. Some vegetables, of 
the cabbage class, require much boiling to make them either 
palatable or digestible. Fruits which might disagree if 
eaten raw may be roasted or stewed or baked, and their 
fibres placed in such a condition by these processes as to 
render them digestible. 

Drinks. — The drinks used by man are either water alone 
or in solutions of various kinds, such as alcoholic wines, 
liquors, etc. ; gaseous or aerated, such as mineral waters ; 

6* E 



66 PHYSIOLOGY. 

acid or saccharine; and infusions, as they are called, such as 
tea and coffee, which are mainly boiling or cold water in 
which these substances have been placed for a brief period 
of time. 

There is no fixed rule to be laid down as to the amount 
of drink necessary for an individual to take in the twenty- 
four hours. Much depends on habit, and some persons can 
take gallons, while others, equally healthy, use but little 
fluid. Whatever the system requires must be taken. Some- 
times solid food is swallowed so rapidly that the saliva of 
the mouth, to which we shall presently refer more minutely, 
cannot soften it. It therefore becomes necessary to swallow 
a considerable amount of fluid, such as water, to produce 
this effect. Should such be the case, or in any event, the 
amount of water or other fluids swallowed at meals should 
be moderate, not excessive, as the food becomes too much 
softened, and the secretions of the stomach so much diluted 
as to be impaired in their efficiency for digestive purposes. 
Acid and sweet drinks, or drinks of any kind, should be 
avoided immediately before meals, as they unduly excite 
the secretions of the stomach before food, the natural stim- 
ulus, is taken. Hot drinks stimulate the stomach to in- 
creased secretion, and at the same time increase the action 
of the muscular coat of that organ ; but habitual stimula- 
tion of this kind is injurious, and must finally weaken it. 

Water. — To be suitable for diet, water should be fresh, 
without smell, and comparatively tasteless. It should con- 
tain a little gas or mineral matter, but without any organic 
matter, such as animal or vegetable life. When taken into 
the body, as in drinking, it replaces what is lost by evap- 
oration from the skin, from the lungs, etc. 

Of the waters used for drinking purposes, rain water 
should be the purest if properly collected ; that is, not 



DIGESTION. 07 

from the roofs of houses, where impurities are apt to exist. 
It is much more insipid than river water, even when pure. 
Spring watei" may contain, in addition, a preparation of 
lime. If it forms a curd with soap, it is called hard water; 
if not, it is called soft water. The latter is preferable for 
domestic uses, as it has more effect in dissolving vegetable 
substances, and is not likely to produce any chemical 
changes. It contains more air than river water, and is 
therefore more sparkling. River water, being obtainable 
in large quantities, is generally used for drinking purposes, 
but is liable to be rendered impure by matters emptied into 
it. Well water may also be injured by impurities filtered 
through its walls, but a properly lined well will protect 
itself from them. Lake water is likely to be unfitted for 
drinking purposes, for into it are poured impurities from 
springs and rivers, such as decayed animal and vegetable 
matter, which may have remained in stagnant waters until 
decomposed and then been emptied into the lake. Foul- 
ness in water may be corrected by filtering through gravel, 
charcoal, etc., or boiling before being filtered, and then 
shaking it to bring back to it some of the air it has lost. 
Impurities may also be driven out by distilling the water ; 
that is, by heating it until it becomes vapor, and then as 
the vapor cools collecting it drop by drop in another vessel. 
Wine is the juice of the grape after it has undergone 
fermentation. To produce a wine it is necessary that there 
be present sugar (or some substance that will form sugar, 
such as starch), water, and a ferment, all exposed to a 
temperature of 70° or 80°. Reel wines are made from the 
juice of the black grape ; white wines, usually from the 
white grape or the dark grape deprived of its outer cover- 
ing. To produce effervescence the wines must be bottled 
before the fermentation is completed. The gas formed is 



68 PHYSIOLOGY. 

carbonic acid, and, being unable to escape, it remains dis- 
solved in the wine until the cork is removed. Sweet wines 
are made so either by the grape-juice originally having an 
excess of sugar in it or from the addition of sugar to it. 
All wines contain in varying quantities alcohol, water, 
mucilage, sugar, coloring-matters, and mineral substances. 
Some of the latter give them their tartness, while the alco- 
hol gives them strength. The proportion of alcohol in 
sherry and port wines is about sixteen to twenty-five per 
cent. — much less, as we shall presently see, than brandy, 
w T hiskey, and gin, all of which contain from fifty to sixty 
per cent. Strong wines deposit in time a crust, which is 
largely tartar, the loss of which makes the wine more 
grateful to the stomach, so that old wine is really made 
better by age. The alcohol and carbonic acid in the wine 
are produced by the gradual action exerted on the sugar 
of the juice of the grape by the albuminous part of the 
grape, which has undergone fermentation. 

The following table gives the percentage of alcohol in 
the more common wines and spirits: 

Port wine 16 to 23 per cent. 

Sherry 16 to 25 " 

Madeira 16 to 22 " 

Champagne 5 to 13 " 

Claret 9 to 13 " 

Hock 6 to 16 

Brandy 50 to 60 

AVhiskey 50 to 60 " 

Rum 60to75 " 

Gin 50 to 60 " 

Malt Liquors. — There is less alcohol and more nutritious 
material in these than in wines, but there is added a bitter 
narcotic principle imparted to them from the hop. They are 
therefore tonic and nutritive, but they are not very digest- 



DIGESTION. 69 

ible. The amount of alcohol in ales and beers varies from 
two to ten per cent., but they contain also gases, acids, 
sugar, bitter matters, etc., according to the article used. 
Malt itself is barley which has been made to germinate by 
warmth and moisture, and afterward dried. Part of the 
albuminous matter of the barley is converted into a fer- 
ment called diastase, which changes a great deal of the 
starch of the seed into grape-sugar or a gum called dex- 
trine. Ale and beer are obtained by fermenting an infusion 
of malt. 

Spirits. — When wines are distilled we procure spirits, 
such as brandy, which is obtained from the wine of the 
grape. Whiskey is obtained from grain — rye, maize, and 
wheat being used for the purpose. In the fermentation 
the starch is converted into sugar, and finally into alcohol 
and carbonic acid gas. Rum is obtained from fermented 
molasses. Gin is distilled from corn and juniper-berries, 
or from some substitute for them. 

It is a strange fact that so many of the different drinks 
used in all parts of the world, such as tea, coifee, cocoa, etc., 
should contain almost identically the same active principle, 
with the same chemical composition. They differ in other 
qualities, for coffee has more aromatic matters in it, and tea 
has tannic acid, which makes it more astringent. Tea and 
coffee stimulate the nervous system, but are not followed by 
the after-depression characteristic of alcoholic stimulants. 
They therefore give prompt relief in cases of fatigue, 
especially the coca-leaves of South America, which the 
inhabitants of that region use for this purpose after excess- 
ive labor and wearisome marches. 

Quantity of Food. — As regards the quantity of food 
which should be taken by any one in health, no exact 
amount can be mentioned, so much depends on the capacity 



70 PHYSIOLOGY. 

and health of the individual, the age and sex, as well as 
the influence of climate. Excess is a great cause of ill 
health, especially if the food be hastily swallowed, and 
hence improperly prepared for digestion. It has been 
estimated by physiologists that the average quantity daily 
consumed by a person in full health is about a pound of 
meat, rather more than that quantity of bread, about a 
quarter of a pound of fat, and between three and four 
pints of water, either taken as such or in the form of milk, 
tea, or other fluids. A larger amount of food is consumed 
in cold than in warm climates, and in cold seasons of the 
year than in hot. It is said that the daily amount of food 
taken by an Esquimaux is twelve to fifteen pounds of 
meat, including a large mass of fat. The case is cited by 
a Russian admiral of an inhabitant of those far northern 
regions who ate, in his presence, twenty-eight pounds of 
boiled rice and butter at a single meal. Mention is made 
by one of the Arctic explorers of an Esquimaux who in 
twenty-four hours devoured thirty-five pounds of meat, in 
addition to a number of tallow candles. 

Children and youth really require, in proportion to their 
size, more nourishment than those who are older ; but the 
aged have often to take more in proportion on account of 
the failure of their digestive organs and their inability to 
get the full benefit of what they eat. Those who take 
exercise require more than those of sedentary habits. 

Meals should be regular and far enough apart to allow 
of full digestion being completed. Some persons require 
much more time than others, but scarcely any more than 
four or five hours of interval. Children can eat at briefer 
intervals than the adult, but the quantity at each meal 
should be moderate, not excessive, so that the stomach will 
not be taxed beyond its powers. Supper should be light, 



DIGESTION. 71 

and, as a rule, without animal food, especially in the case 
of children, as the circulation may be interfered with by 
a full supper, particularly before going to bed, and the 
brain be disturbed so much as to cause dreams or rest- 
lessness. 

Change, rather in the nature than the quantity of the 
diet, is desirable. The strong require a different kind of 
diet from the weak, and the occupation or pursuit in life 
has also to be considered. Those who are engaged in heavy 
and fatiguing labor should eat more food and articles of a 
more substantial character than those who are devoted to 
literary work. Delicate persons and those with weak 
digestive powers should avoid articles that are not easily 
digested, and depend on light but nutritive diet taken in 
small quantities and frequently repeated. Bread and milk, 
with meat in moderation, and a small amount of vegetable 
food with fruits, form a good diet for such persons. As 
will be hereafter stated, food should not be hastily swal- 
lowed, as the action of the teeth in dividing the food, and 
of the saliva in softening it, will not then take place. 

Conditions Necessary for a Healthy Diet. — These may be 
briefly stated : 

1. The food taken must contain a proper proportion of 
the different principles that already exist in the human 
body. 

2. It must correspond in quantity and quality with the 
amount of work performed by the individual himself to 
supply the matter and force spent by him. 

3. It must have flavor or taste to render it palatable, 
and therefore more digestible. 

In addition to these conditions, it must not be forgotten 
that the influence of climate, such as temperature, affects 
the activity of digestion, as well as the quantity of food to 



72 PHYSIOLOGY. 

be taken. In a cold climate exercise renders the appetite 
brisk, and a larger amount of food is required ; there is 
also an increased demand for internal heat, so that fatty 
matters are necessary as food, which produce when oxidized 
a large quantity of heat. 

Appetite and Hunger. — Hunger is an internal sensation, 
always referred to the stomach. In its slightest manifesta- 
tion it is simply appetite, or an artificial desire for food. 
It may be temporarily relieved by substances that are not 
nutritious, or by emotion, and is increased by moderate 
mental and physical exercise. The sensation of hunger 
occurs after the stomach has been for a while empty, di- 
gestion being accomplished. Hunger arises from a real 
want of the system. It is more powerful in childhood and 
youth, and also in old age after the digestive powers have 
begun to give way. The sensation seems to be the result 
of a nervous impression made upon the stomach from the 
needs of the other organs for nourishment. When death 
occurs from protracted hunger, the young and robust die 
before those who are older, the activity of all the functions 
being greater in them, and the necessity for food being 
therefore more imperative.* Hunger is an irresistible de- 
sire that cannot be disappointed. If no food is taken the 



* Dante in the Inferno describes the sufferings and death from hunger 
of the Count Ugolino, and shows a correct knowledge of the more serious 
effects of abstinence from food on the young than on the old ; although 
on this latter point physiologists differ: — 

"Now when our fourth sad morning was renewed 
Gaddo fell at my feet, outstretched and cold. 
Crying, 'Wilt thou not, father, give me food?' 

There did he die. and as thine eyes behold 
Me now, so saw I three fall, one by one, 

On the fifth day and sixth ; whence in that hold 
I, now grown blind, over each lifeless son 
Stretched forth mine arms." 



DIGESTION. 73 

tissues of the body break down, and the individual is com- 
pelled to live on himself, as new materials for the nourish- 
ment of the body, not being obtained from without, must 
be derived through the blood from all organized parts of 
the body. The result is, that the harmony of action of the 
various organs is broken up; the functions of the body, 
such as digestion, absorption, preservation of its heat, and, 
finally, respiration and circulation, gradually cease, and 
death takes place. The blood, changed in its character, 
is not fit to nourish, the brain therefore suffers, and the 
person thus affected often becomes delirious before death. 
He may die of cold, for the food necessary to keep up the 
temperature of the body has not been supplied to it. 

It has been supposed by some that hunger was caused by 
the coats of the stomach rubbing against one another ; but 
this is not probable, as there can be but little friction be- 
tween walls made up of such flexible membrane. Others 
have imagined that hunger is excited by the presence of 
gastric juice, as the secretion of the stomach is called, which 
irritates the lining of that organ and gives rise to the de- 
sire ; but this is not so, for experiments have shown that 
during fasting no gastric juice is poured out in the in- 
terior of the stomach. Hunger is a vital action beyond 
our powers to fathom, being the expression of an internal 
want. 

The vegetable exhibits something much akin to hunger, 
and, if we may so call it, we must believe that this sensa- 
tion can sometimes exist without the necessity of a nervous 
system, for the vegetable is devoid of all nervous apparatus. 
The plant being fixed in the soil, its rootlets go out in all 
directions in search of the food which it requires. This 
action seems to resemble the promptings of hunger in the 
animal, for it is the evidence of a desire for food dependent 

7 



74 PHYSIOLOGY. 

on the wants of the system. There must be a supply to 
take the place of what has been expended. 

Thirst. — Thirst is a local sensation, referred to the throat, 
being a desire for liquid nourishment. It is characterized 
by a feeling of dryness of the lining membrane of the 
throat, caused by a positive want of fluid on the part of 
the system from a diminished amount of water in the blood 
from any cause, such as increased secretion of perspiration, 
etc.; from arrest of secretion of fluid from the lining mem- 
brane of the stomach or intestines; or from emotion. A 
certain amount of fluid taken daily is essential to perfect 
health. Thirst is more imperative than hunger, and death 
results from it more rapidly, as has been observed in the 
cases of the shipwrecked. Salty articles of food produce 
thirst, because they require a large supply of watery fluid 
for their solution, derived through the Avails of the ali- 
mentary canal, and thus the amount of water in the blood 
is diminished. Thirst may sometimes be relieved tempo- 
rarily by bathing, as in salt water, a sufficient amount of 
fluid passing through the pores of the skin. It is said that 
after the second day of deprivation of water the most ter- 
rible suffering ensues, and that death will usually result in 
from seven to ten days. It is not easy to state how long a 
human being can exist without drink, so much depends on 
the state of the system at the time, the condition of the 
atmosphere, etc. It is said that an animal will live longer 
on water alone than on any dry principles of food. 

Apparatus for Digestion. — The simplest form of digest- 
ive apparatus is that of the vegetable, which receives its 
nourishment directly from the earth through its roots or 
by its leaves from the surrounding air. The food it thus 
obtains requires no preparation, as in the animal, which 
necessarily possesses an internal arrangement of organs 



DIGESTION. 75 

adapted to the purpose. In the very lowest form of animal 
life a simple sac or cell, without any opening whatever, is 
all that exists for the entire digestive process ; there is no 
stomach, for none is required ; everything is at once absorbed. 

In another form of low life the whole animal is a sort 
of sac, with only one opening, thus resembling a delicate 
gum-bottle. The animal is all stomach, and like a mem- 
branous bottle can be turned inside out ; the former inner 
surface will soon become like the external, and absorption 
will take place from the new interior surface. In the 
infusory animalculse, as they are called, which are micro- 
scopic animals found in various fluids, the same general 
type exists, on a simple scale, as in man ; there is a body 
having an opening for the reception of food, a dilated part 
or reservoir like a stomach, with an open canal leading 
from it. As we rise higher in the scale the apparatus 
becomes much more complicated, according to the nature 
of the food on which the animal lives. When the organs 
of digestion are developed to their fullest extent, as in 
man and the higher classes of animals, they include a 
cavity or series of cavities in which the nutritious portion 
of the food is prepared for absorption, and the non-nutritious 
portions of food are expelled. In man, the apparatus of 
digestion consists of a long canal, varying greatly at differ- 
ent parts in size and structure. It is usually divided into 
the following parts : mouth, pharynx, oesophagus or gullet, 
stomach, and intestines. The stomach and intestines occupy 
the greater part of the abdo'men, and are the chief organs 
interested in the process of digestion. 

The mouth receives the food, which is here subjected to 
the action of the teeth and of certain juices which are 
poured into that cavity to soften and dissolve it. The 
tongue, cheeks, and jaw by their movements also aid in 



76 PHYSIOLOGY. 

producing changes in the size and character of the particles 
of the food. The fluid poured into the mouth is called 
the sali'va, which is formed by little bodies called saVivary 
glands. } the fluid being carried from them by small canals 
or ducts passing from the glands and opening into the 
mouth. This process is called insal' iva s tion. The action of 
the teeth in cutting, crushing, or grinding the food is called 
mast ica't ion. The food thus becomes finely divided or 
comminuted. Connected with the jaws are muscles, which 
are very large in some animals, as the horse, through which 
additional force is exerted in mastication. 

The Teeth. — The teeth are composed of a material like 
bone, called the dent'ine or ivory, and are inserted deeply 
into the jaws by roots or fangs. The portion of the tooth 
above the gum is called the crown, which is covered by a 
thin layer of enamel, the hardest material in the body. In 
the interior of the tooth is a cavity containing nerves and 
bloodvessels. The young child when it gets its first set of 
small teeth complete — the temporary or milk teeth — has 
twenty in all — four inci'sors, two cani'nes, and four mo'- 
lars in each jaw. This early set is developed before birth, 
but cuts through the gums at the following ages : incisors, 
seventh to ninth month; canines, eighteenth month ; molars, 
twelfth to twenty-fourth month. When the child grows to 
be six or seven years old their roots are absorbed, and the 
teeth are loosened and fall out, to give place to the perma- 
nent teeth. These are thirty-two in number — sixteen in 
each jaw — arranged in each half jaw as follows : two in- 
cisors, one canine or dog-tooth, two bicuspids (having two 
points or cusps), and three molars or grinders (from mola, 
"a mill"). The permanent teeth are developed in the jaw 
below the milk teeth, and both are found at the same time, 
about the fifth year of age. They gradually push out the 



DIGESTION. 



77 



milk teeth from that time of life until the twelfth or four- 
teenth year of age. The appearance of each of these sets 
will be seen in the accompanying illustrations (Figs. 16, 17). 




Opening for passage of nerves and bloodvessels. 
Fig. 16. — General View of the Teeth. 

The " wisdom-tooth/' so called on account of its not making 
its appearance until the twentieth or twenty-first year of 
life, is the third molar tooth of each jaw. 

The teeth are of such shape in various "animals as to be 



78 



PHYSIOLOGY. 



adapted to the special food on which they live. The sharper 
teeth in front are called inci'sors, from their cutting proper- 
ties, and the canine because they are like those of the dog. 
The motions of the jaw also admit of a cutting or crushing 
action upon the food. In animals which live entirely on 
animal food the jaws are very strong, and move more 




5" 4" 3" 2" 

Fig. 17. — Teetii of FirtsT and Second Dentition. 

V to 5' are the teeth of first dentition, or milk-teeth ; 1" to 8" are teeth of 
second dentition, or permanent teeth. 

readily up and down than from side to side, as mastication 
is not necessary. The muscles of the jaw are also very 
strong, and the cutting teeth are much more decidedly 
developed than those for crushing, the latter being sharper 
than in other animals. By an inspection of a single tooth 
we can usually decide the nature of the animal, and the 
naturalist can even build upon this tooth, as a basis, a plan 
of the animal's general structure, habits, etc. 



DIGESTION. 



79 





An animal which feeds entirely on flesh is called car- 
niv'orous (euro, camis } "flesh/' 
and voi'o, " I eat "). One that 
eats grain is called graminiv'- 
orous ; one that lives on grass, 
herbiv'orous. Man, with teeth 
and digestive apparatus adapted 

to all kinds of food, is Called Fig. 18. -Teeth of Insect-eating 
• / / • cc 11 y) i Animal. 

ommv orous (omms, all, and 

voro, "I eat"). Animals which feed entirely on insects 
(insectivorous) have conical-pointed teeth, 
which fit closely into one another in the 
two jaws like the teeth of clock-work (Fig. 
18). Those animals which exist mainly 
on fruits (fragiv' orous) have the teeth 
rounded rather than sharp (Fig. 19). The 
grain-eating or graminivorous animals, 
whose food requires crushing or bruising rather than cut 
ting, have large flat teeth, which, like 
millstones, crush and break up the 
food into fine particles by the side-to- "^^^^^liiil 
side movement of the jaws (Fig. 20). FlG - 20.— Teeth of Grain 
These teeth have been called molars EATING An,mal ' 

(from mola, " a mill "), on account of this very action, 
the carnivorous animal (Fig. 21) 
the molars are sharper, and so 
placed as to meet like scissors- 
blades, while the canine teeth are 
largely developed. In the horse, 
the sharp front incisor teeth of 
other animals become more like 
the molars in structure and 
shape. Almost all animals have 



Fig. 19.— Teeth of 
Fruit-eating Ani- 
mal. 




Ill 




Fig. 21.- 



Teeth of Flesh-eating 
Animal. 



80 PHYSIOLOGY. 

molar teeth in some form or other. The teeth of the ele- 
phant are entirely molar. Some animals, as the whale, are 
entirely devoid of teeth. In man, the teeth occupy an in- 
termediate place between the carnivorous and herbivorous 
animal ; of his thirty-two teeth, twelve correspond to those 
of the carnivorous and twenty to those of the herbivorous. 
The movement of his jaws is upward and downward and 
sideways. 

The Tongue. — The tongue assists in mastication by en- 
abling the particles of food to be worked around in the 
mouth, to be acted upon by the various juices poured into 
it. In some of the lower animals the tongue acts as a 
means of seizing upon their prey, which is to them their 
main source of nourishment. While man uses his hands 
to convey food to his mouth, the elephant is provided with 
an extension of the snout, called the trunk, which lias 
powers of suction with which it can carry articles into its 
mouth. Insects have feelers around the mouth for similar 
purposes. In some animals the motion of the tongue in 
the mouth enables them to suck in liquid food, just as the 
same process is effected in man. Juices are thus imbibed 
by insects through tubes or suckers. 

The Salivary Glands. — These glands (Fig. 22) are found 
on each side of the mouth in man, and are four in num- 
ber. They pour out a thin and a thicker kind of fluid, 
which becomes mixed with that secreted by the membrane 
lining the mouth. Although saliva is being constantly 
formed and swallowed, the presence of food in the mouth 
excites these glands to increased action, and an additional 
quantity of saliva flows into that cavity. Even the mere 
sight of agreeable food often has this effect, which is well 
known as " mouth-watering." The amount of saliva se- 
creted varies with the kind of food. If it is hard or dry 



DIGESTION. 



81 



a larger quantity is poured out. It was found by experi- 
ment on horses that 400 parts of saliva were mingled with 
every 100 parts of hay, but only 50 parts of saliva were 
furnished when 100 parts of green stalks and leaves were 
taken. The saliva softens and moistens the food, and eon- 




Fig. 22. — Salivary Glands. 

1, parotid gland; 2, sublingual gland; 3, submaxillary gland; a, nerve; c, d, e, 

muscles of face and neck; /, lower jaw ; g, artery. 

verts the starchy matter contained in it into a gummy sub- 
stance called dex'trine, and afterward into grape-sugar. This, 
being soluble, is more easily absorbed. It seems that this 
power depends on the admixture of the mucus of the mouth 
with the saliva. Perfect mastication, or division of the 
food, and perfect insalivation are necessary to ensure per- 
fect digestion in the stomach. The structure of the salivary 

E 




82 PHYSIOLOGY. 

glands, when examined under the microscope, resembles a 
bunch of grapes. Their ap- 
pearance is shown in Fig. 23. 
The average amount of saliva 
secreted in the course of twenty- 
four hours lias been estimated at ^^^^^^^^^^^W^ 
from two to three pounds. The ( %2^& ctwoSyB^ 
terms parot'id, sub max' Mary, 
and sublingual, applied to the 
salivary glands, merely mean, 
from their derivation, that they Fl0< 2 3.-Structtjrb of a Salivary 
are near the ear, under the jaw, Gland. 

or under the tongue, as will be seen in Fig. 22. 

Deglutition. — When the food has undergone these pro- 
cesses in the mouth it is swallowed. Swallowing, or deglu- 
tition, as it is technically called, includes the passage of the 
alimentary mass from the back part of the mouth into the 
stomach, and requires the action of the mouth, throat or 
pharynx, and the oesophagus. 

The pharynx and oesophagus together form a muscular 
canal extending from the mouth to the stomach (Fig. 24). 
The cavities of the mouth, nose, and larynx open into the 
pharynx. The pharynx is separated from the mouth by a 
fold of muscle and membrane called the ve'lura, or soft 
palate. The oesophagus is about nine inches long, and, 
like the pharynx, is lined with mucous membrane and sup- 
plied with a muscular coat. The first part of the act of 
swallowing is under the control of the will, but after this 
is accomplished the passage of the food from the throat to 
the stomach is entirely involuntary. This is a wise pro- 
vision, for otherwise the particles swallowed might pass 
into the upper opening of the air-passages, as they occa- 
sionally do when, in common language, they " go the 



DIGESTION. 



83 



wrong way." During the act of swallowing the larynx 
is elevated by the muscles connected with it, and removed 
out of the way of the mass of food. The passage from 

r 




10—& 



Fig. 24. — General View of Mouth, Pharynx, etc. 

1, canal from t hroat to middle ear ; 2, back part of nose ; 3, soft palate ; 4, soft palate 
covering tonsil; 5, tonsil; 6, base of tongue ; 7, epiglottis; 8, part of cartilage 
of larynx; 9, laryngeal portion of pharynx; 10, cavity of larynx; 11, nasal 
fossae; 12, vault of the palate, or roof of mouth; 13, 14, tongue; 15, muscle be- 
neath tongue; 16, hyoid bone; 17, interior of larynx; 18, 19, thyroid cartilage. 



84 PHYSIOLOGY. 

the back part of the throat into the nose is also closed by 
muscular contraction, so that fluids cannot get into that 
cavity. There is a cartilaginous body called the epiglot'tis, 
which is situated at the upper part of the larynx, behind 
the base of the tongue, and when the food is swallowed it 
covers the glottis, as the opening in the larynx is called, 
and thus aids in preventing the mass from getting into the 
air-passages. The passage into the stomach is effected first 
by the very rapid and convulsive contraction of the muscles 
of the throat or pharynx, and of other muscles which 
remove the larynx, or upper part of the air-tube, out of 
reach, and give a smooth surface for the food to pass over. 
In this way it reaches the oesophagus or gullet, which also 
contracts around it, forcing it into the stomach. The lower 
part of this tube remains contracted for a while after the 
entrance of the food into the stomach, so as to prevent its 
return upward. 

Processes of Digestion. — The first step of digestion is 
called prelien'sion of the food, which really denotes nothing 
more than taking the solid or liquid food into the mouth. 
It therefore requires no elaborate description. Digestion 
in the mouth is called o'ral or bue'eal digestion (os,oris, or 
buccfij "a mouth"), including the action of the salivary 
glands, the teeth, etc., already described. Deglutition, or 
swallowing, is the next step of the process, after which 
come, in immediate succession, stomachal and intestinal 
digestion. 

When the food is hastily swallowed — and this is gene- 
rally called "bolting the food" — the cutting and crush- 
ing action of the teeth is not effected, and the alimentary 
substance is swallowed in a state unfitted for perfect diges- 
tion in the stomach, so that dyspepsia or indigestion may 
result, especially if this neglect becomes habitual. Some 



DIGESTION. 85 

of the salivary glands pour out a thinner fluid than the 
others — the thicker secretion facilitating the progress of 
the alimentary mass, or bolus as it is called, when swal- 
lowed, while the thinner helps to dissolve it. The im- 
portant chemical change which takes place in the mouth, 
however, is the conversion of starchy matters in the food 
into dextrine and grape-sugar. This is effected by means of 
a ferment called ptyalin (pron. ty'alin, from a Greek word 
meaning saliva), which is present in that fluid. If the 
food escapes this action through hasty swallowing or other 
cause, another fluid which is poured into the intestines, 
called the pancreatic juice, or juice of the pancreas, exerts 
a similar effect upon it after it has passed out of the 
stomach. No detention of thin fluids takes place in the 
mouth ; they are not acted upon in that cavity, but in the 
stomach. In the case of drinking, fluids are usually sucked 
into the mouth and swallowed without any action upon 
them in that cavity. When the lips are applied to a cup 
the air is drawn inward by inspiring or breathing in, and 
the liquid flows into it. 

As ptyalin is the ferment of the mouth, so do we have 
also a similar ferment in the secretion of the stomach, 
called pep'sin, but endowed with different powers, and in 
the pancreatic juice, pan'creatin, which exerts the effect 
already alluded to on starchy matters. 

The voluntary and involuntary steps in the process of 
deglutition to which reference lias been made show that 
there must be two separate divisions of the nervous system 
regulating it. This Ave find to be the case. When we 
come to consider the general subject of the Nervous System 
we shall find that it has its divisions into a voluntary and 
an involuntary nervous apparatus, the former alone being 
under the control of the brain. The moment the food 

8 



86 



PHYSIOLOGY. 



passes over the top of the windpipe to the oesophagus, the 
involuntary system comes into play. Otherwise respira- 
tion would be seriously interfered with, and danger to life 
result. The process of deglutition also includes the passage 
of the food along the oesophagus. 

Digestion in the Stomach and Intestines. — When the food 
reaches the stomach it is subjected to entirely new processes, 



Gall-bladder 



Large intestine 



Caecum 



Vermiform 
appendix. 




Spleen. 



Colon. 



-7— Small intestine. 
- Colon. 



Small intestine. Rectum. 

Fig. 25. — Alimentary Canal. 



both chemical and mechanical . Here it remains for a greater 
or less time, according to its digestibility. The stomach 



DIGESTION. 



87 



and intestinal canal of man occupy a medium place be- 
tween the carnivorous and herbivorous animal, resembling 
the latter rather than the former. In the carnivorous the 
animal food is easily digested, and the alimentary canal is 
not, therefore, long, as the food requires a very short stay 
in the stomach and in those parts 
of the intestines concerned in 
active absorption. Herbivorous 
animals require a great deal of 
digestion of the food before it 
becomes fit to be absorbed, and 
the canal is therefore long, and 
some parts of the intestine are 
very capacious. The stomach is 
also large in these animals and 
complicated in structure, so as to 
receive and digest food that is 
bulky without being greatly nu- 
tritious. Some of these animals 
have as many as four stomachs. 
In man the stomach is the 
most dilated part of the diges- 
tive apparatus, and is in shape 
like the ordinary bagpipe. It 
lies across the upper part of the 
abdomen, and is separated from 
the chest, in which the heart and 
lungs are placed, by a thick muscle, called the diaphragm 
(Fig. 26), which covers the whole width of the floor of 
the chest. The opening in the stomach at its left end 
is for the entrance of the oesophagus. It is opened and 
closed by a muscular arrangement. The opening at the 
right side is the point at which the food passes into the 




Fig. 26.- 



-The Thorax and 

Abdomen. 



1, thorax, or cavity for heart and 
lungs; 2, diaphragm ;3, ahdonien ; 
4, spinal column ; 5, spinal canal. 



88 



PHYSIOLOGY. 



intestine, which here begins its course. The left end of the 
stomach is called the card'iac extremity, because it is near 
the heart, or splenic, because it is near the spleen ; the other, 
the pyWric (from pylorus, " a janitor"), because of the ex- 
istence of a kind of valve here which, like a janitor, will 
not ordinarily allow the food to pass into the intestine until 
properly prepared to do so. The stomach is lined by a 




Fig. 27. — Intetuob of thk Stomach. 
P, pylorus; E, oesophagus; C, cardiac orifice of the stomach. 

membrane (Fig. 27) secreting a fluid called mucus, and 
hence called a mucous membrane. The mucous membrane 
is not smooth, but is thrown into numerous folds. It is 
continuous from the inner edge of the lips through the 
whole alimentary canal. This mucus keeps the membrane 
always moist, and is the only fluid secreted when the stom- 
ach is empty. • 

When any article passes into that organ, however, a 
peculiar colorless fluid is poured into the interior of the 
stomach, called the gastric juice. It is chiefly water, but 



DIGESTION. 89 

contains an acid — by some considered lactic acid, by others 




Fig. 28. — Muscular Fibres of the Stomach. 
1, circular fibres; 2, oblique fibres. 

hydrochloric — and a ferment, to which the name of pepsin 
has been given. The internal surface of the stomach pre- 
sents a network of mi- .2 
nute ridges, in the 
spaces between which 
the mouths of little 
glands open. The en- 
tire structure is per- 
meated with minute 
vessels, which enter 3 
these ridges and send 5 
numerous branches 4 
around these glands. 
Many little glands of 
different sizes and 
shapes are found in all 
parts of the stomach, but especially at the upper part. 




1 

Fig. 29. 

1, 2, 3, pits in mucous membrnne of stomach ; 

4, f>, orifices of the glands. 



90 



PHYSIOLOGY. 




They pour out a thin kind of fluid, and contribute their 
share to the formation of the juices that assist in diges- 
tion by the moisture they create. This 
fluid is always present, but the gastric 
juice, so called, is probably secreted more 
profusely in that part of the stomach 
lying in close vicinity to the intestine, 
and only after food is taken. The glands 
secreting the gastric juice are tubular in 
character (Fig. 30) and lined with cells. 
J> They are found more at the lower part 
of the organ. 

The muscular coat of the stomach (Fig. 
Fig. 30.— Gland from 28) is outside the mucous one, but in con- 
Pvlor.c portion op ^ with k The contractions of the stom- 

Stomach (magniLed). 

i.ductor canal; 2, P ri n - acll > whit ' h produce the churning move- 
cipai branches; 3,ter- ment so necessary to perfect digestion, are 

minal portion. , , n i i 

clue to the presence ot the muscular coat, 
which is made up of fibres running in different directions. 
Some are longitudinal, some oblique, others circular. The 
effect is to contract it in every direction. Should all these 
fibres contract at the same time, the stomach would be forcibly 
emptied, the food being expelled from it. The longitudinal 
fibres, acting alone, contract or shorten the 
stomach. The circular fibres, especially at 
the pylorus, press on the contents of the 
stomach, and cause the food to pass from 
one end to the other. The bloodvessels 
and nerves of the stomach are more nu- 
merous than those of any other organ of the body. The 
effect of the contraction of the oblique fibres in changing 
the shape of the stomach is well exhibited in Fig. 31, the 
organ being divided into two distinct portions. The outer 




DIGESTION. 



91 



coat of the stomach — the serous — is a delicate structure, 
not concerned in stomachal digestion. 

Stomachs of other Animals. — In man the stomach is not 



CEsophagus 




Duodenum 



Pylorus. 



C 33 GO 

Fig. 32. — Stomachs of a Sheep. 



S--- - 



as small as in the carnivorous animal. In the herbivorous 
the stomach is very complicated. In the ox, for example, 

Oesophagus-. 

Oesophageal groove. 

Manyplies 



Rennet 



Duodenum 




Fig. 33. — Stomachs of a Sheep (interior). 

there are four distinct divisions, all of which are interested 
in the digestive process, but of which the fourth is the 



92 



PHYSIOLOGY. 



only one resembling the human stomach. Some of these 
animals have the power of returning the food from the 
second stomach to the mouth to be ru f ruinated, as it is 



Gizzard 




Liver. 



Gall-bladder, 
Bile-ducts. 



Pancreas 



Fig. 34.— Digestive Apparatus of Domestic Fowl. 

called, or chewed over again ; and when it comes down again 
it passes directly into the third stomach without entering 
the first and second. The peculiar arrangement of a sheep's 
stomach is shown in Figs. 32, 33. In birds, in which 
grain or seed is swallowed whole, and therefore unfit for 



1) Hi EST ION. 93 

digestion, a sac called a crop (Fig. 34) exists, in which 
fluid is poured out to aid in its digestion. There is also 
another small cavity or second stomach, which leads into a 
third stomach or gizzard, a kind of paunch connected with 
the alimentary canal proper. This organ is a powerful 
muscular arrangement, a thick sac with a small cavity con- 
taining a number of pebbles, which seem to take the place 
of teeth, and by their mill-stone action crush the food by 
trituration or grinding. In birds of prey the crop is less 
developed. In carnivorous or flesh-eating birds the giz- 
zard is not so powerful an organ as in grain-eating birds, 
and the alimentary canal is altogether much more simple, 
as the food does not require so much digestion. In some 
of them the stomach is merely a sac of muscles and mem- 
branes, and pours out a powerful secretion to act upon the 
food. This is all the more necessary as the animal does 
not possess any arrangement for mastication, and it is essen- 
tial that the digestive organs shall be packed away in a 
small space, so that its flight will not be interfered with. 

In reptiles, a class of animals which is capable of ab- 
staining from food for a long time, there is generally a 
mouth of large capacity, Avith teeth that form a part of the 
jaw itself, or, like tortoises, their jaws are horny ; the 
stomach varies in size and shape, and the intestines are 
usually short. 

In fishes, those which feed on the blood and juices 
sucked from other animals have their mouths, teeth, and 
tongue arranged and acting upon the principle of the cup- 
ping apparatus of the surgeon. In all the liver is large, 
the stomach and intestines varying in size, and digestion 
being performed quite rapidly. 

Insects (Fig. 35) vary in the arrangement of their di- 
gestive apparatus, as in their nutriment. Some feed on 



94 



PHYSIOLOGY. 



the juices, others on the solid parts, of both plants and 
animals. Where it is necessary to cut the food, as in the 
case of the grasshopper, a cutting arrangement exists, in 
addition to feelers, a tongue, etc. In herbivorous insects, 
the digestive apparatus is considerably developed and com- 
plicated. There are really three stomachs — a crop, gizzard, 




Fig. 35. — Digestive Apparatus op Insects. 

A, Mole Cricket.— a, head and appendages ; ft, salivary glands ; c, secreting grannies 

of the same glands; d, feelers; e, cardiac part of stomach ; /, accessory ponclies 
of the stomach ; g, middle part of stomach ; //, pyloric part of stomach ; i, intes- 
tines; k, canals representing liver. 

B, Bee. — a, head and month ; ft, salivary glands ; c, oesophagus ; e, crop : h, stomach ; 

ft, canals representing liver. 



and stomach proper. The alimentary canal, including the 
intestines, is not straight, but generally tortuous, with en- 
largements and contractions at various points. In those 
which live chiefly on animal food the canal is short, and 
in those which feed on vegetable substances the canal is 
longer. This we have already seen to be true of animals 
much higher in the scale. 



DIGESTION. 



95 



111 all forms of animal life there is a stomach in some 
shape or other, although it may be, in its simplest expres- 
sion, nothing more than a mere expansion or sac, through 
which all digestive and nutritive absorption is effected. 
In some of the very lowest animals, indeed, as already 
stated, an intestinal canal is wholly absent, the expansion 
referred to taking the place and performing the duties of 
both stomach and intestines. 

The variety of forms of stomach characteristic of dif- 
ferent types of animals is well shown in Fig. 36 : 




Fig. 36. — Stomachs of Various Animals. 

A, sheep ; B, hyena; C, hamster: D. seal ; E, salmon, a, cardiac opening of 
oesophagus; b, pyloric opening. 

Action of the Stomach in Digestion. — When the food 
enters the stomach to be digested, that organ gradually 
becomes distended, especially in its muscular coat, so as to 
occupy a much larger space in the abdomen. The dila- 
tation takes place chiefly forward and upward and to the 
left, so that the stomach experiences a movement of rota- 
tion. When it becomes overloaded it may press upward 
against the floor of the chest, so as to make respiration 
laborious. A regular series of contractions and relaxations 
of the stomach takes place under the exciting presence of 
food — regularly and alternately from left to right, from the 
opening of entrance to that of departure, and then in the 
opposite direction. The result is the admixture of the 



96 PHYSIOLOGY. 

food with the fluids secreted in the stomach, and the bring- 
ing of fresh portions under their influence. From the 
time of entrance of food into the stomach at the cardiac 
extremity until its appearance at the pylorus, when ready 
to make its exit into the intestine, the contents of the 
stomach are undergoing a regular revolution or churning 
process, each revolution taking perhaps from one to three 
minutes in its accomplishment. The diaphragm, the large 
muscle separating the chest from the abdomen (Figs. 26,49), 
by its powerful contractions also presses upon the stomach 
and increases its action. The movement of the stomach and 
also of the intestines has been considered so worm-like in 
its character as well to deserve the name vermicular (vermes, 
"a worm") assigned to it. Stomachal digestion may there- 
fore be said to include, as its two important elements, this 
gentle motion of the organ and admixture with its fluids. 

Changes in the Food in Digestion. — The name chyme 
(pron. time) has been given to the soft, pulpy, semi-fluid 
mass undergoing digestion in the stomach. It is no longer 
the food proper, but food combined with secretions from the 
salivary erlands and the stomach. It of course diifers in 
character with the nature of the food taken, the amount of 
liquid which may have been swallowed, and with the stage 
of the digestive process at which it is examined. Saliva is 
probably poured into the stomach from the mouth during 
the whole of stomachal digestion. If the food taken has 
been starchy, it is probable that some of it has undergone 
conversion in the mouth, as previously stated; but some 
of it that was unconverted will be acted upon by the saliva 
in the stomach, or may pass into the intestine without fur- 
ther change. Fatty matters also wait there unchanged, to 
be digested after they leave the stomach. 

Other materials, such as the albuminous, fibrinous, etc., 



DIGESTION. 97 

of which meat is composed, undergo their digestion in the 
stomach itself. Besides all these there will be found a 
variety of indigestible matters which are of no use to the 
system, and must eventually be thrown out of the canal. 
In the decomposition of the food acids will be formed 
which have no part in the digestive process, such as acetic 
acid from fermentation of the sugar, etc. All kinds of 
food are not, therefore, wholly digested in the stomach. 
Oily matters undergo digestion in the intestine, and as a 
rule vegetable food also awaits its exit from the stomach to 
seek the action of the intestine. Thick fluids, such as 
soups, may be acted upon in both regions. 

Animal food is more digestible than vegetable on account 
of the peculiar arrangement of its fibres. Animal fats and 
other oils are not only indigestible in the stomach, but they 
interfere with the process of digestion there, and are not 
themselves easily digested" when they pass into the intes- 
tine. Bread, potatoes, and pastry are partly digested in 
the stomach and partly in the intestine. Liquid substances, 
as will be shown hereafter, are generally absorbed by the 
bloodvessels of the stomach at once if sufficiently thin. 

The length of time required for digestion of the food in 
the stomach, under favorable circumstances, is two to four 
hours, but this period is lengthened in those who are of 
languid and sedentary habits, and in those who do not take 
the proper amount of exercise. While the food is in the 
stomach it is exposed to a temperature of at least 100° 
Fahr. Under the influence of all these agencies — gastric 
juice, acids, heat, etc. — the animal food is converted into 
a modified form of albumen, called peptone or album inose, 
which is capable of more ready absorption than albumen. 
The active principle of the gastric juice — pepsin, obtained 
from it by chemical action — is the important medium 

' 9 G 



98 PHYSIOLOGY. 

through which these changes are effected. The gastric 
juice is a powerful antiseptic ; that is, it will check the 
putrefaction of substances like meat. The main result, 
therefore, of stomachal digestion is the transformation of 
alimentary matter into chyme, and the change effected upon 
animal food. The action is both chemical and mechanical. 

Action on Thin Fluids. — Certain thin fluids furnish 
neither chyme nor chyle, being essentially composed of 
water, or water mixed with alcohol or other materials. 
Although really a variety of Absorption, which we shall 
soon consider, we may briefly allude to this subject under 
the head of Digestion. These enter the stomach without 
being subjected to any action in the mouth, and are ab- 
sorbed by the veins of the stomach without undergoing 
any other action, and by the veins of the small intestine. 
The veins into which they enter unite with other veins to 
form what is called the por'tal vein, which goes directly to 
the liver. After a short stay there this blood passes into 
the current of the blood to the heart and through the system 
generally. Not being digested, but passing rapidly into 
the circulation, we can understand why the effect of alcohol 
is so soon felt when taken into the stomach, and why the 
liver should become diseased in those who drink liquor to 
excess. Other nutritious substances, if in very fine solu- 
tion, also probably pass into the same veins without being 
subjected to the process of digestion. 

Digestibility of Food. — Substances are said to be very 
digestible or easy of digestion if they are known to make 
but a short stay in the stomach ; but some of these very 
articles may not be nutritious, and may be difficult of 
digestion in some healthy but peculiarly constituted 
stomachs. The terms nutritious and digestible do not, 
therefore, imply the same thing. It seems to be the rule 






DIGESTION. 99 

that substances which are capable of affording nourishment 
are detained for a longer time in the stomach than others, 
as if that organ were endowed with a power or sense of 
choosing what is best for it. Some materials, as crude 
vegetables, oils, and fats, will soon pass out of the stomach 
without being digested there at all. It has been contended 
by some that tables showing digestibility of various articles 
of food seem to exhibit only how long each remains in the 
stomach, but they do not prove the exact degree of digesti- 
bility. Milk probaby disappears from the stomach very 
rapidly. It is said by one writer that an hour after it is 
swallowed there are scarcely any traces of it in the stomach ; 
but milk is composed not only of sugar, water, and salts, 
all of which may be absorbed in that time, but it also con- 
tains fatty matter, which is not so easily gotten rid of. It 
is estimated that five or six pounds of gastric juice are 
secreted daily. 

Aids to Digestion. — Proper digestion is rendered more 
probable by rest of mind, agreeable mental and gentle 
physical exercise, as well as by variety of food. Over- 
exertion of any kind should be avoided soon after taking 
a full meal. The recumbent posture should not be indulged 
at such times, and prolonged sleep should be deferred until 
after digestion has been accomplished. If indulged in at 
all, a short nap may be taken in a sitting posture. Diges- 
tion in the earliest periods of life may be impaired by the 
tendency to excess of acid in the stomach, but usually the 
digestive powers of young persons are better than those of 
adults, considering the food which they are each capable 
of taking. Where articles disagree, the fashion has often 
been to say that the individual is bil'ious ; but such a term 
conveys no idea whether there is too much or too little 
bile poured into the intestine for digestive purposes. Of 



100 PHYSIOLOGY. 

course under irritation of food that is indigestible the liver 
may be excited to renewed energy, and the action of the 
muscles of the upper part of the intestine may be inverted 
and bile be brought into the stomach. 

In regard to taking fluids at meals, if they are not stimu- 
lants the habit should be regulated by the inclination. With 
some persons little or no drink at such times is necessary, 
and drink can be taken between meals. It is certainly an 
error of diet to wash down every portion of solid food 
with liquids, as is the habit of some. A moderate quantity 
of liquid is generally desirable, and after the gastric juice 
has ceased to act it may be excited to action by a fresh sup- 
ply of water. It is thought by many conducive to health 
to take a glass of pure water in the morning before break- 
fast. Exercise before breakfast disagrees with many a 
weak stomach and produces a languid feeling all the day. 
Long walks before the morning meal are not attended with 
beneficial results as often as the devotees of systematic train- 
ing claim for them. 

Length of Time required. — The following table gives the 
result of experiments to determine the length of time which 
some of the more commonly employed articles of food oc- 
cupy before their disappearance from the stomach. This 
represents, to some extent, their digestibility, and also the 
effect of cooking upon the substances named: 

Hon;-;. hours. 

Apples, raw 2 Butter, melted 3.30 

Barley, boiled 2 Cabbage, raw *2.30 

Beef, roasted 3 " with vinegar 2 

Beefsteak, broiled 3 " boiled 4.30 

Beef, fried 4 Cake, corn, baked 3 

Beets, boiled 3.45 " sponge, baked 2.30 

Brains, ai^iraal, boiled 1.45 Catfish, fried 3.30 

Bread, corn, baked 3.15 l Cheese, old, strong 3.30 

" wheat, baked 3.30 | Chicken, fricasseed 2.45 



DIGESTION. 



101 



hours. 

Corn and beans, boiled 3.45 

Costard, baked 2.45 

Duck, roasted 4 

Dumpling, apple, boiled 3 

Eggs, bard boiled 3.30 

'■ soft boiled 3 

" fried 3.30 

" roasted 2.15 

" raw 2 

Fowls, boiled 4 

" roasted 4 

Goose, roasted 2.30 

Lamb, boiled 2.30 

Milk, boiled 2 

11 raw 2.15 

Mutton, roasted 3.15 

" broiled , 3 

boiled.. 3 

Oysters, raw .. 2.55 

" roasted 3.15 

stewed 3.30 

Pig, roasted 2.30 

Pigs' feet, soused 1 



HOURS. 

Pork, roasted 5.15 

" salted and fried 4.15 

Potatoes, Irish, boiled 3.30 

" roasted 2.30 

Rice, boiled 1 

Salmon, salted 4 

Soup, barley, boiled 1.30 

" bean 3.30 

" cbicken 3 

" mutton 3.30 

" oyster 3.30 

Tapioca, boiled 2 

Tripe, soused , 1 

Trout, salmon, boiled.. 1.30 

" " fried 1.30 

Turkey, roast 2.30 

boiled . 2.20 

Turnips, boiled 3.30 

Veal, broiled 4 

" fried 4.30 

Vegetables and meat, hashed.. 2.30 

Venison steak 1.35 



Digestion in the Intestines. — The intestines are a contin- 
uous canal, leading directly from the stomach. They vary 
in length in different animals, and are usually divided into 
the small and the large intestines. The small intestine (Fig. 
37) is a narrow flexible tube about twenty feet long, coiled 
upon itself, and divided into three parts — the duode'mim, 
so called from its length being estimated at twelve fingers' 
breadths (duodeni, " twelve ") ; the jeju'rmm (jejunus, 
" empty "), so called from its usually being found empty 
after death ; and the il'eum (from a Greek word meaning 
" to twist," on account of its convolutions). It is in these 
portions of the intestine that intestinal digestion chiefly 
takes place. The large intestine, which is intended rather 



102 



PHYSIOLOGY. 



as a receptacle for the useless and undigested portions of 
the food, is divided into the ece'eum or blind sac (emeus, 
" blind "), the co'lon, and the rec'tum (rectus, " straight "). 
The intestines have similar coats to the other parts of the 
canal, being lined with mucous membrane, which is covered 
by a muscular coat, and this again by a serous coat, here 




Fig. 37 — General View of the Intestines. 

1, duodenum ; 2, small intestine; 3, large intestine; 4, ileum ; 5, appendix; 

(), rectum ; 7, colon ; 8, stomach ; 9, diaphragm (cut). 

called the peritone/um. The same vermicular or worm-like 
movement of alternate contraction and dilatation takes place 
here as in the stomach. This is beyond the control of the 
will, and is excited by the presence of food. The circular 
muscular fibres contract the intestine in its calibre, and the 
longitudinal fibres shorten it in its length. 

The arrangement of the intestines in the lower animals 
is somewhat different. In man there is a small pouch con- 






DIGESTION. 



103 



nected with the caecum, called the appendix , which is of no 
practical use whatever, but it seems to be left there to show 
a similarity in original structure in the animal series. In 




Fig. 38. — The Large Intestine (opened). 

1, duodenum ; 2, ileum, connecting with small intestine ; 3, jejunum ; 4, 4, 4, colon ; 
5, caecum; 6, valve between ileum and caecum ; 7, appendix; 8, rectum. 

some animals it is so large as to be really a distinct intes- 
tine. In birds that eat grain or that feed on all kinds of 
food there are two csecums. In reptiles the intestines are 
short, and there is but little difference in size between the 



104 



PHYSIOLOGY. 



large and small intestines. In insects the intestinal canal is 
often considerably developed and more complicated than in 
some of the upper classes of animals. 
In fishes the pancreas is absent, but 
is sometimes replaced by csecums 
around the pylorus (Fig. 39). 

Intestinal Juices. — In man the 
mucous membrane of the intestines 
is thrown into permanent folds, so 
as to give a large surface for ab- 
sorption, and bloodvessels, absorb- 
ent vessels, and nerves are largely 
distributed in them. Here, too, on 
the mucous membrane is poured oat 
a fluid called the intestinal juice, 
which is secreted by an immense 
number of little bodies or glands. 
It has been estimated that there are 
many thousands of these little se- 
creting bodies, or fol'licles as they 
are called, engaged in this duty in 
a single individual. Two anato- 
mists, named Brunner and Lieber- 
kiihn, first described these little 
glands, which are now called, after them, the glands of 
Brunner and Lieberkuhn. This is not the only fluid poured 
into the intestine, for at a distance of four or five fingers' 
breadths from the pylorus there open into the duodenum 
two canals, which bring bile from the liver and gall-bladder, 
and a fluid called the pancreatic juice from an organ called 
the pancreas, or abdominal sweetbread, as it is sometimes 
called, lying close to the stomach. Both of these fluids aid in 
the digestion of the food in that portion of the intestine. The 




Fig. 39. — Intestine of Bony 
Fish (Mackerel). 

a, oesophagus ; b, stomach ; c, py 
loric csecums: d, intestines. 



DIGESTION. 



105 




arrangement of the panereas 
and the opening of its canal 
into the intestine are shown 
in Fig. 41. 

It has been estimated that 
more than twenty pounds of 
digestive fluids are secreted in 
the twenty-four hours at dif- 
ferent parts of the apparatus 
for digestion : 

Pounds. 

Saliva 3J J Pancreatic juice 

Bile 3^ | Intestinal juice J 

Gastric juice 14 

It seems worthy of remark that the food is acted upon 
in the mouth by an alkaline material ; in the stomach by 



Frc 40. — Tubular Glan 
testine (magnified 100 



ns of In- 

times). 



Pounds. 
.. 2" 




Fig. 41. — The Pancreas, 

Divided, so as to show— 1, pancreatic duct or canal; 2, canal emptying into 
intestine; 3, duodenum. 

an acid ; in the pancreatic fluid again by an alkaline fluid. 
This alternate chemical action is doubtless connected with 
the perfecting of the digestive process, although not easy 
to explain. 

When the valve between the stomach and intestines 



106 PHYSIOLOGY. 

allows the food to pass, after digestion in the stomach 
has been effected, the muscles of the latter organ drive 
it out into the duodenum or first part of the intestine. 
This valve — the pylo'rus — is not at all under the control 
of the will, and acts wholly under the stimulus of the 
food. 

In the duodenum the food is mixed with the bile and 
pancreatic juice, and with the intestinal juice already re- 
ferred to. The effect of the pancreatic fluid on the food is 
to make a mixture, resembling what the apothecary calls 
an emulsion, by the admixture of fatty or oily matters with 
other ingredients. When this emulsion is made by the 
action of the pancreatic juice on oily or fatty food that has 
escaped digestion in the stomach, it is more easily absorbed 
for the useful purposes it has to subserve in the system. 
Besides this, the starchy parts of the food that were not 
converted into grape-sugar in the mouth undergo this 
change when brought into contact with the pancreatic 
juice. This fluid also has some action on albuminous 
matters akin to that exerted by the gastric juice. 

The bile is secreted by the liver, an organ lying under 
the diaphragm, above the stomach. This is a very large 
organ, weighing three or four pounds, and measuring about 
ten or twelve inches in width. Only a small part of the 
bile formed by it and poured into the intestine is of use in 
digestion ; the rest of it passes along with the refuse food. 
Bile is one of the chief agents in the digestion of fats. 
There is a sac connected with the liver called the gall- 
bladder (Fig. 25), and this acts as a receptacle for the bile. 
The canal from this and the one from the liver unite, so as 
to pour the bile from each together into the intestine. The 
gall-bladder is indeed filled from the duct or canal from 
the liver before it discharges itself, drop by drop, into the 



DIGESTION. 107 

canal common to the two. While food is undergoing diges- 
tion in the stomach the bile from the gall-bladder, as if by 
a telegraphic signal from the stomach, begins to come down 
into the intestine, to be ready for its duty when the chyme 
or digestive mass arrives. This, for want of a better term, 
is said to take place by sympathy, and the fact has been 
proved, like many others here detailed, by experiments 
made, in the interests of science, upon living animals. It 
seems remarkable that so large a quantity of bile should 
be poured into the intestine when we can ascribe to it so 
little efficacy in the digestive process. It seems as if the 
bile also acts as a stimulant on the mucous and muscular 
coats of the intestines. 

Action of the Intestines.— The vermicular action of the 
intestines, sometimes called the peristal' tic action, passes the 
food slowly onward from one portion to another. The 
mixture of intestinal fluids with food forms a milky fluid, 
called chyle (pron. kile, from a Greek word meaning "juice"). 
The process by which it is formed is called chyl' ification. 
As has been stated, the mucous membrane of the intestine 
is thrown into folds, and numerous small projections occur 
in these (Fig. 42), called villi. In these commence a series 
of vessels, called chylif erous vessels, because they carry away 
the chyle, or lac'teals, because the fluid they contain is milky 
in appearance (lac, " milk "). As will be described under 
the head of Absorption, the chyle is absorbed into these 
vessels and carried directly into the blood. The intestinal 
juice proper, it is thought, has very little effect other than 
that of moistening the food. It is not acid, like the gastric 
juice, and being alkaline it gradually neutralizes the acidity 
of the latter, and thus prevents fermentation and decompo- 
sition of the food. By the time that the food has reached 
the large intestine all the nutritive matter has been taken 



108 PHYSIOLOGY. 

from it. Digestion proper may be said, therefore, to be 
virtually ended with the small intestine. 

A certain amount of air is always present in the in- 
testines, dependent chiefly on the chemical changes in the 
food during digestion. The air existing in the stomach 
contains oxygen, but this chemical element is not usually 
found in the intestines. 

"With this sketch of the process of digestion the reader 
can readily appreciate the manner in which nourishment is 
disposed of to meet the wants of the body. Nearly all the 
food taken into the mouth is digested in one form or an- 
other. To sum up the results at which we have arrived, 
we may briefly say that when solid food is taken it is dis- 
posed of as follows : the starchy matters are converted in 
the mouth and stomach, by the action of the saliva, into 
grape-sugar, and also by the pancreatic juice in the small 
intestine ; fatty matters are chiefly digested in the small 
intestine by the pancreatic juice and bile together, being 
made into an emulsion for easy absorption by the chylif- 
erous vessels ; albuminous matters, such as meat, are acted 
upon by the gastric fluids. 



QU ESTIONS. 
What is digestion? 

In what part of the body is it effected ? 
Why does food require to be digested? 
How is the general system affected by such a process? 
What general action on the food takes place during digestion? 
Through what circulating fluid is the body nourished? 
What is the process called by which the digested food is carried into 
the blood? 

Is digestion simply confined to animal life? 

How is food supplied to the vegetable? 

What chemical element of the plant is derived from the soil? 



DIGESTION. 109 

Plow can the soil be rendered more porous? 

In what way is the plant nourished? 

From what source is the food of man derived? 

What is an aliment? 

What is chyle? 

Are any other substances used as food except those derived from the 
animal and vegetable kingdoms ? 

How is the growth of the body effected in early life? 

Why does growth remain stationary in adult life ? 

On general principles, what ingredients are best adapted for food ? 

What simple article may be mentioned as an example? 

What special articles of diet resemble the blood in composition? 

What ingredients do they possess in common ? 

Through what fluid is the system largely supplied with mineral 
matters? 

What substances are included under condiments? 

What effect has salt upon the process of digestion ? 

In what part of the body does lime exist? 

What are the principal chemical substances found in the body? 

Which of these is most important as a constituent of the blood? 

What is the average amount of iron in the human body? 

Of what two chemical substances is starch composed ? 

What other articles of diet have the same composition ? 

What articles of food are mainly composed of starch? 

What articles furnish cane-sugar? 

What substances furnish grape-sugar ? 

In what organs of the body do we find sugar, and what kind? 

In what form are fatty substances taken as food ? 

What are nitrogtnized aliments? Albuminous? 

From what part of mineral food are they derived ? 

Are they found in vegetables? 

What is the effect of acid drinks in digestion? 

Into what two classes has food been divided? 

Which predominates in animals? 

Why is nitrogen important as an element of food? 

Why does a horse consume more food, in proportion to its weight, 
than a dog? 

What is the effect on animals of restriction to one class of food ? 

Why can they thrive on milk alone? 

What disease arises from want of variety in diet? 

On what principle are diet-tables for the army and navy founded? 
10 



110 PHYSIOLOGY. 

From what are oils and fats derived ? 

What three chemical substances are found in them ? 

What is the sweet principle of fats called ? 

What is the difference between an oil and a fat? 

What is the appearance of oily matter under the microscope? 

What is an emulsion? 

What important fluid is an example of an emulsion ? 

In what part of the world are oily matters taken largely as articles of 
food ? Why ? 

From what sources is sugar derived? 

In what form do vegetables and fruits present it? 

What are the digestive qualities of sugar : ; 

What varieties of sugar are usually employed? 

What is the purest form of starch ? 

With what other substance is it mixed in oats? Beans? Peas? Po- 
tatoes? Almonds? 

From what substances is starch prepared artificially? 

Is starch soluble? 

What is said of gum as an article of food ? 

What are the three classes of albuminous substances? 

From what does albumen derive its name? 

In what substances is it found? 

What is the chief ingredient in a bird's e^s;? 

In what part of the body do we find fibrin in a fluid state? 

AVh at is gluten? 

How is it obtained from wheaten flour? 

To what does bread owe its porous character? 

What are the principal ingredients of gluten? 

In what important fluid do we find casein? 

What is curds and whey ? 

What is rennet ? 

What chemical substance is specially characteristic of albuminous 
articles? 

With what other substances should they be combined in a properly- 
mixed diet? 

State from the table the main ingredients in bread, rice, milk, 
flour. 

What is gelatin, and how is it obtained ? 

What is the effect of restricting an animal to one kind of food ? 

What portion of animals is generally employed for food? 

Why was blood prohibited as an article of diet for the Hebrews ? 



DIGESTION. Ill 

What is the objection to the use of pork as an article of food ? 

What circumstances affect the character of animal food? 

What element exists to a marked extent in the flesh of young animals? 

What difference is there in young and older animals as to the rela- 
tions of fat and flesh? 

How is the flesh of animals affected by season ? 

Why are fat animals more desirable as sources of food? 

What effect has the juice of the stomach on putrid substances? 

What parts of birds are used as food? 

What effect has exercise on the quality of the flesh of birds? 

What are the principal ingredients of the flesh of fish? 

What relation does it bear in, its nutritive properties to a meat or a 
vegetable diet? 

What term is applied to fish-eating tribes? 

What chemical element in the flesh of fish rendeis that kind of food 
desirable in some conditions of the brain? 

Why is milk well adapted to the nourishment of the body? 

What change takes place in milk after it is taken into the stomach ? 

What becomes of the curd? Of the whey? 

Why does the cheesy part of milk sometimes disagree? 

How can milk be made more digestible? 

What articles are derived from milk? 

What are the constituents of cream, and why is it less digestible than 
milk ? 

What is butter, and why is it not very digestible ? 

What is cheese? Buttermilk? 

Why is buttermilk more digestible? 

What is koumyss? 

Into what two parts is the egg divisible ? Which has the most albu- 
men? Which is most digestible? 

What effect has heat upon the albumen ? 

What advantage has the egg as an article of diet? 

Why are fried eggs less digestible? 

What is an herbivorous animal ? 

How does an animal obtain nitrogen ? 

From what is bread usually made ? 

Of what is it chiefly composed ? 

What is leavened bread? 

What is the effect of a ferment like yeast? 

What changes take place in milk from fermentation ? In bread ? 

What is said of the digestibility of cakes and pastry? 



112 PHYSIOLOGY. 

From what other flours is bread made ? 
How does bread aid the digestion of soup? 
Why is stale bread more digestible than fresh? 
What rule should be observed in regard to eating fruit? 
How do preserved fruits act on the digestive organs? 
On what does the value of food depend ? 
What effect has cooking upon food? 
In what way does it render it more digestible? 
What are the limits of temperature for cooked meats? 
What is the effect of roasting on meat? 
What is broiling, and what effect has it on meat? 
What changes take place in meat when boiled? 
What effect have baking and stewing? 
Why are fried meats less digestible? 
What effect has cooking upon vegetables? 
What are the principal drinks used by man? 

What rule should be observed as to the amount of drink to be taken 
in the day or at meals? 

What effect have drinks taken immediately before meals? 

How do hot drinks affect the stomach ? 

What qualities should water possess for drinking purposes? 

What does the drinking of water replace in the system? : - 

What kinds of water are used for drinking purposes ? 

What is the purest form of water? 

What is the difference between hard water and soft water? 

Which of these is preferable for cooking purposes? 

Why is spring water more sparkling? 

Why is well water less pure? 

Why is lake water generally unfitted for drinking purposes? 

How can foul water be rendered purer? 

What is distilled water? 

What is wine? 

To produce a wine, what materials must be present ? 

How do red wines differ from white? 

What produces effervescence in wines? 

How are sweet wines made? 

What are the chief ingredients of wine? 

To which ingredient is its strength due? 

What is the proportion of alcohol in wines? In spirits? 

Why is old wine more desirable? 

How are the alcohol and carbonic acid produced in wines? 



DIGESTION. 113 

How do malt liquors differ from wines? 

What proportion of alcohol do they contain? 

"What is malt, and how are ales and beers derived from it? 

What is the ferment, and how does it act? 

How are spirits produced from wines? 

What is brandy ? Whiskey ? Rum ? Gin ? 

How do coffee, tea, cocoa, etc. resemble each other ? 

How do coffee and tea differ ? 

What is the difference in effect on the system of these and alcoholic 
drinks? 

On what does the quantity of food to be taken depend ? 

What is the estimate of the quantity of meat, bread, fat, and water 
daily consumed by a person in full health? 

W 7 hat effect has temperature on the amount? 

At what period of life is more food required ? 

What effect has exercise ? 

What rules should be observed as to meals ? 

Why are late or meat suppers objectionable? 

How should the diet of those with weak digestive powers be regulated ? 

W T hat processes are interfered with by hasty swallowing of the food? 

What three conditions are necessary for a healthy diet? 

How is the internal heat of the body kept up in cold climates? 

What is the natural desire for food called ? The artificial desire? 

To what organ is the sensation referred ? 

When does it occur? 

At what age is it most urgent ? 

W 7 hat is the cause of hunger? 

What is the effect of protracted hunger on the system generally ? 

Which of the functions give way last? 

In what way does the brain suffer? 

What action of the stomach has been wrongly assigned as the cause 
of hunger? W r hy does this not explain it? 

What is the fluid poured into the stomach during digestion called ? 

How do we know that this is not the cause of hunger ? 

Is the expression of hunger restricted to the animal? 

In what way does the plant exhibit it? 

What is thirst? 

What are the causes of the sensation ? 

Is thirst or hunger more imperative? 

Why does salty food increase the thirst ? 

Can thirst be relieved by external means? 
10 * H 



114 PHYSIOLOGY. 

When does death usually result from protracted thirst? 

"What is the simplest form of digestive apparatus? 

What is the simplest arrangement in the animal? 

What do we next find as we rise a step higher in the animal scale? 

What is the digestive arrangement in the infusory animalcule? 

What is the general arrangement for digestion in man and the higher 
classes of animals ? 

Into what parts is it divided in man? 

Which of the organs named occupy the abdomen? 

To what action is the food subjected in the mouth? 

What is the fluid poured into the mouth called ? 

What name is given to the organs producing the saliva ? 

What is insalivation ? 

What is the action of the teeth upon the food called? 

How is their action incrensed in some animals? 

What is the chief material in teeth? 

What are the different parts of a tooth called? 

What do we find in the interior of a tooth? 

What are the earliest teeth called, and how many are they ? 

How do we divide them? 

When does each kind make its appearance? 

What change takes place in the teeth about six or seven years of age? 

How many permanent teeth are there? 

How are they arranged? 

What are the wisdom-teeth? 

Why are incisors so called? 

Why are canine teeth so called? 

What is the arrangement of the jaws and teeth in animals that live 
on flesh? 

What information may we learn from a single tooth? 

What is a carnivorous animal ? 

What term is applied to an animal that feeds on grain? To grass- 
eating animals? 

What is an omnivorous animal? An insectivorous animal? 

What is the arrangement of the teeth in the insectivorous animal ? 

What is a frugivorous animal, and what is the peculiarity of its 
teeth? Of the grain-eating animal? 

What name is applied to the grinding teeth? 

What animal has molar teeth almost exclusively? 

What relation do the teeth of man bear to the herbivorous and car- 
nivorous animal ? 



DIGESTION. 115 

What action has the tongue in digestion? 

What other action do the tongues of animals exert? 

What is the arrangement in the elephant for taking food? In insects? 

Where are the salivary glands situate? 

What is their number, and what do they pour out? 

What effect has the presence of food in the mouth upon these glands? 

What is mouth-watering? 

Is the quantity of saliva affected by the kind of food? 

What changes take place in the food from the action of the saliva? 

Is digestion in the stomach assisted by such action in the mouth ? 

What is the interior structure of the salivary glands as seen under the 
microscope ? 

How much saliva is secreted in the twenty-four hours? 

What is meant by the terms parotid, submaxillary, and sublingual ap- 
plied to the salivary glands? 

What is the process of deglutition ? 

What organs are concerned in deglutition ? 

After the food leaves' the mouth' into what cavity does it pass? 

What other cavities open into the pharynx? 

What is the soft palate? 

W T hat canal leads from the pharynx to the stomach? 

How long is it ? 

What kind of membrane lines it? 

What part of the act of swallowing is under the control of the will? 
Which is involuntary? 

Why is this last a wise provision of Nature? 

How does the act of swallowing affect the movement of the larynx? 

Why does not food pass into the cavity of the nose when swallowed ? 

What is the epiglottis, and how does it protect the larynx at such a 
time ? 

What action takes place just as food reaches the stomach? 

How do the pharynx and oesophagus aid in propelling the food down- 
ward toward the stomach ? 

What is the first step in the process of digestion ? 

What terms denote digestion in the mouth? 

What is the next stage of the process of digestion after deglutition? 

What is meant by bolting the food? What effect has it upon di- 
gestion ? 

Do all the salivary glands pour out the same kind of fluid? 

What chemical change takes place in food in the mouth ? 

What is the ferment called which produces this change? 



116 PHYSIOLOGY. 

What other fluid in the intestine has a similar effect on food? 

Where does action take place on this fluid ? 

What other ferments do we find in the alimentary canal? 

How is deglutition controlled by the nervous system? 

At what stage does the involuntary nervous system control it ? 

How long does food remain in the stomach ? 

What relation do the stomach and intestines of man bear to those of 
the carnivora and herbivora? 

Which of these two classes requires the shortest and simplest canal 
for digestive purposes ? Why ? 

Why is the apparatus long and complicated in the herbivorous animal ? 

What class of animals has a number of stomachs? How many? 

What is the shape of the human stomach ? 

What relation does it bear to the chest ? 

What muscle separates the two? 

How many openings has the stomach ? 

At which side does the food pass from the stomach into the intestine? 

Which is the cardiac extremity? The splenic extremity? The 
pyloric extremity ? 

What kind of membrane lines the stomach? 

What kind of fluid does it secrete? 

What is the appearance of this membrane? 

How far does it extend in the alimentary canal ? 

What effect has the mucus upon this membrane? 

What fluid is secreted in the stomach when it is empty? 

What fluid is poured into the stomach when food is introduced into it? 

Of what ingredients is the gastric juice composed? 

What is the acid in the gastric juice? 

By what means are. the gastric juices secreted? 

What is the shape of the glands secreting the gastric juice proper? 

At which end of the stomach is it most largely secreted ? 

What is the appearance of the interior surface of the stomach ? 

What action is exerted by the muscular coat of the stomach? 

AVhat is the arrangement of its muscular fibres? 

When all these fibres contract together, what effect have they upon the 
stomach? 

When the longitudinal fibres act alone, what is the result? 

When the circular fibres act alone, what effect have they on the 
stomach ? 

How is the shape of the stomach affected by the contraction of the 
oblique fibres? 



DIGESTION. 117 

What kind of membrane is the outer coat of the stomach ? 

In the herbivorous animal with four stomachs, which one of these 
resembles the human stomach ? 

What is rumination? 

Which stomachs of animals are interested in it? 

"What is the arrangement for digestion in birds? 

What is the gizzard, and in what class of birds is it chiefly developed ? 
What is its action ? 

What is the digestive arrangement in insects? 

In carnivorous birds what is the form of the digestive apparatus? 
What action takes place in the stomach ? 

What is the peculiarity of the digestive organs in reptiles? In fishes ? 

What is the nature of the food of insects? 

What is the arrangement of the digestive organs in herbivorous 
insects ? In carnivorous ? 

What is the simplest form of stomach in the lower animals? 

What change takes place in the stomach when food enters it? 

In what direction does the dilatation take place? 

What kind of movement does the stomach undergo? 

How may respiration be affected by it? 

What is the result of the regular contraction and dilatation of the 
stomach in digestion? 

Describe the churning movement of that organ. 

How long a time is occupied by each revolution? 

What effect has the diaphragm in digestion? 

What is meant by the vermicular movement of the stomach and 
intestines? 

What are the two important features of stomachal digestion? 

What is chyme? 

Is it always the same fluid? 

How is its composition affected ? 

Is any action exerted by the saliva on the contents of the stomach ? 

What classes of substances are digested in the stomach? 

How may acids be developed in the stomach? 

Where do oily matters chiefly undergo digestion ? Yegeiable food? 

Where are thick fluids, as soup, acted upon ? 

Why is animal food more digestible than vegetable food? 

What effect have animal fats and oils on digestion? 

Where are bread, potatoes, and pastry digested? 

"What becomes of thin liquids taken into the stomach ? 

How long a time does digestion in the stomach occupy ? 



118 PHYSIOLOGY. 

Under what circumstances is this period prolonged? 

To what temperature is food exposed in the stomach? 

What change is effected in albuminous matters under the influence of 
the gastric juice, acids, and heat? 

What is the active medium through which it is effected? 

What is meant by the antiseptic action of the gastric juice? 

What may be summed up as the result of stomachal digestion ? 

Through what vein do they pass to the liver? 

Where does this blood go after leaving the liver? 

Why is the effect of alcoholic drinks so rapid? 

Why is the liver affected in drunkards? 

When are substances said to be digestible? 

What relation does digestibility bear to the nutritive qualities of arti- 
cles of food ? 

What is learned from tables of digestibility of food ? 

What is said of the digestibility of milk? 

What quantity of gastric juice is secreted in the twenty-four hours? 

How is healthy digestion affected by mental or physical exercise? 

What precautions should be taken after meals? 

How is digestion impaired in early life? 

What is the condition called "bilious," and how is it excited? 

What rule should be adopted in regard to taking fluids at meals? 

What error of diet is committed in this respect? 

What is the effect of water on the gastric juice? 

What facts do we learn from the table of digestibility, as it is called? 

Into what part of the alimentary canal does the stomach empty? 

Into what two great divisions are the intestines divided? 

What is the length of the small intestine? 

Into what parts is it divided? 

Why is the duodenum so called ? The jejunum ? The ileum ? 

Is intestinal digestion effected in the small or large intestine? 

What is the use of the large intestine? 

Into what parts is the large intestine divided? 

Why is the caecum so called ? 

What are the coats covering the intestines? 

What is the serous coat called ? 

What kind of movement takes place in the intestines? 

Is it voluntary or involuntary? 

What effect is produced by contraction of the circular fibres? 

What is the effect of contraction of the longitudinal fibres? 

What is the appendix of the caecum, and what is its use? 



DIGESTION. 119 

What peculiarity does the cnecum present in grain-eating birds? 

What peculiar arrangement of the intestines in reptiles? In insects? 

What is the appearance of the lining membrane of the intestines in man ? 

What is the arrangement for absorption ? 

What fluid is poured out on the mucous membrane? 

How is it secreted ? 

After what anatomists are the intestinal glands named? 

What two important fluids are poured into the duodenum? 

What is the total amount of digestive fluids secreted in the twenty- 
four hours? 

How much saliva? Bile? Gastric juice? Pancreatic juice? In- 
testinal juice? 

Which of these fluids is alkaline? 

What is the action of the pylorus? 

Is it under the control of the will ? 

With what juices is the food mixed in the duodenum ? 

What effect has the pancreatic fluid on oily or fatty matters? 

What effect on starchy matters? 

What organ secretes the bile ? 

What is the situation of the liver, its weight and width ? 

Is all the bile used for digestive purposes ? 

On what portions of the food does the bile act ? 

What organ contains the bile, and what connection has it with the 
liver ? 

What effect has digestion in the stomach upon the bile? 

What effect has bile on the coats of the intestine? 

What is the peristaltic action of the intestines? 

W T hat is chyle? 

What is the process called by whicli it is formed? 

What are the villi? 

What vessels take their origin from them? 

Why are they called lacteals? 

What effect has the intestinal juice on the food ? 

Is the intestinal juice acid or alkaline? 

How does it prevent fermentation of the food ? 

When may digestion proper be said to be terminated? 

To what is the presence of air in the intestine usually due? 

To sum up the steps in the process of digestion, where does action take 
place on starchy matters ? On fatty matters? On albuminous matters? 



ABSORPTION 



Various Forms of Absorption.— Having completed the 
study of the digestion of food, we now consider the process 
by which it is converted to the uses of the system. Under 
the subject of Absorption, in other words, we describe the 
process by which alimentary and other substances are intro- 
duced into the blood. The absorption of thin fluids by the 

bloodvessels in the stom- 
ach, already referred to, is 
an illustration ; and the 
veins of the intestine have 
similar powers of absorp- 
tion. Allusion has also 
been made to the arrange- 
ment of villi in the small 
intestine, containing lac- 
teal (so called from their 
lar fibres, milky appearance) or chy- 
liferous or chyle-bearing 
vessels and bloodvessels, 
both of which absorb 
fluids. Another form of 
absorbent vessel is that 
which is engaged everywhere in removing worn-out parts 
which have done their duty, so to speak. These are very 
numerous, and are called the lymphatic vessels, the fluid 

120 




Areolar tis- 
sue. 

Circular mu: 



Longitudi- 
nal mus- 
cular fibres. 



Fig. 42. — Section of the 
Small Intestine, as seen 
under the microscope. 



ABSORPTION. 



121 



they contain being called lymph, and this is also carried 
directly into the blood. 

Intestinal Absorption. — The lining membrane of the 
small intestine, which we have already stated to be a 
mucous membrane, is thrown into folds, so that the extent 
of its surface is very much increased, in reality doubled. 
A much larger space is thus obtained for absorption than 
would otherwise exist. In addition to this increased sur- 
face there are villi, or delicate elevations on the surface of 
the mucous membrane of the intestine, 
so closely placed together as to give it 
a fine velvety appearance (Fig. 42). In 
each villus, as already stated, is a net- 
work of small vessels, thoroughly sup- 
plied with blood, and a chyliferous 
vessel (Fig. 43). The nutritious por- 
tions of the food are absorbed into the 
villi through a process which is gen- 
erally known as imbibition, which has 
already been referred to under the sub- 
ject of Digestion. These villi dip into 
the cavity of the intestine, and come in 
contact with the materials that have 
already been digested. 

It is well known that when two different liquids — milk 
and water, for example — are separated from one another 
by a membrane, two currents are established in opposite 
directions through the pores of this membrane, but in dif- 
ferent degrees. The experiment can be shown by placing 
milk in a tightly-closed bladder and suspending it in a 
goblet of water; it will be found that the water will 
gradually become milky, and the milk will become thor- 
oughly diluted with the water. The same condition exists 
li 




b c b 

Fig. 43. — One of the 
Villi of the Intes- 
tine, AS SEEN UNDER 

the Microscope. 

a, layer of cells ; b, artery 
and vein ; c, commence- 
ment of lacteal vessel. 



122 



PHYSIOLOGY. 



in the intestines. The lacteal vessels do not have open 

months to suck up the chyle, but absorb it through the 

membrane covering them, on the principle just mentioned. 

After entering the lacteals, which are really a part of 



< H 




..Chyliferous vessels. 
.-Intestine. 



Fig. 44. — Lacteal 0:1 Chyliferous Vessels of the Intestine. 

the lymphatic system, and contain lymph when digestion 
is not going on, the chyle is emptied into the thoracic canal 
or duct (Figs. 44, 45, 46), a long canal which passes along 
the back part of the chest, in front of the spinal column, 
and carries the chyle up to the left side of the neck to 
empty it into one of the large bloodvessels in that region. 
On the way between the intestine and the thoracic canal it 



ABSORPTION. 



123 



passes through a number of small bodies, called lymphatic 
(/lands (Figs. 44, 45, 46), which produce changes upon it 
that render it more like the blood with which it is to be 
mixed. When once mixed with the blood, it passes with 
that fluid to the heart. 

To sum up, therefore, the action of absorption of chyle, 
we may repeat that it is* absorbed either, if very thin, 
through the bloodvessels of the intestine, passing to the 




Fig. 45. — General Plan of Digestive Absorption. 

1, intestine; 2, bloodvessels: 3, portal vein ; 4, liver; 5, veins of liver ; 6, chyliferous 
vessels; 7, lymphatic glands; 8, thoracic duct; 9, venous system. 

liver through the portal vein, or by the lacteals and the 
thoracic duct to the veins of the neck. (This is clearly 
exhibited in Fig. 45, which is intended to be an imaginary 
outline plan or model of the parts represented in Fig. 44.) 
The chyle becomes more and more unlike itself and more 
like the circulating blood as it passes along with that fluid 
for the nourishment of the body. It will be remembered 
that various changes were effected on food in the process 
of digestion in the stomach and intestines. The work of 
the chyliferous vessels is to absorb the fatty matters which 



124 



PHYSIOLOGY. 



we have shown to be made into an emulsion by the juices 
of the intestine; those albuminous matters which resulted 
from the action of the gastric juice on meats ; and such 
portions of sugar as have been converted from starchy 
matters. The veins of the intestine also absorb some of 



. A 




Fig. 46. — Thoracic Duct and Chyliferous Vessels. 

1, thoracic duct ; 2, its lower part ; 3, termination in the vein ; 4, lymphatic 
ganglions; 5, 6, veins of the right side. 

the soluble products of digestion, but not the fatty portions. 
It must not be forgotten, also, that the veins of the stomach 
also absorb thin fluids in a similar way. 

Lymphatics. — This system of vessels penetrates almost 
all parts of the body, receiving by absorption the various 
materials collected from the wear and tear of the system. 



ABSORPTION. 



125 



The vessels are on the surface or deep-seated (Figs. 47, 48). 
After these materials are elaborated in the little bodies 
called lymphatic glands, which are 
found everywhere in the course of 
these vessels, the fluid resulting, 
which is colorless and transparent, 
is carried to be emptied into the 
blood. These lymphatic or absorb- 
ent vessels are very numerous in 
almost every part of the body, and 
run into one another like streams 
into a river, gradually forming 
vessels of considerable size, which 
finally unite and either empty into 
the thoracic duct, in front of and 
parallel to the spinal column, or on 
the right side of the body into a 
large canal called the right lymph- 
atic trunk. Both of these empty the 
lymph into the current of blood. At 
various points in the interior of the 
lymphatic vessels there are projec- 
tions called valves, which prevent the 
lymph from flowing backward in its 
course. The arrangement is similar 
to that of the veins, which we shall 
hereafter describe and illustrate. 

The whole plan of lymphatic 
vessels and lymphatic glands is a 

System of drainage similar to that Fig. 47.— Lymphatic Vessels 
i -i . .f . 1 • i on the Surface op the Ai^r. 

employed m some soils, m which 

the water drained from boggy lands forms channels, which 

unite to make larger streams, still increasing in size, and 




126 



PHYSIOLOGY. 



occasionally expanding into pools, where fresh supplies of 
material are absorbed, and at last pouring into the river or 
open sea. The fluid is carried onward in the lymphatic 
vessels by the powers of contraction of these vessels and 
by the presence of valves, which prevent the lymph from 
flowing backward. When the muscles engaged in breathing, 
walking, etc. contract or expand, they press upon these 

vessels in all parts of the 
body, and assist the flow 
of fluid in them. The 
breathing of air outward 
and inward during res- 
piration also exerts a 
similar influence. 

In some animals, as 
the frog, there is an en- 
largement, with muscu- 
lar fibres connected with 
it, called a lymphatic 
heart, which propels the 
lymph very much in 
the same way that the 
heart itself maintains 
the circulation of the 
blood. In fishes and 
reptiles the lymphatic vessels are of larger size, propor- 
tionately, than they are in man or birds. Birds have two 
thoracic ducts. The lymphatic glands are more numerous 
in man and the upper classes of animals than in any others. 
In those animals which are called invertebrate because 
they have no vertebra or backbone, as the shell-fish, 
spiders, etc., there are no lymphatic or chyliferous vessels. 
In some of these the digested food at once becomes blood ; 




Fig. 48.— Deep Lymphatics of the Finger. 
1,1, deep network of lymphatic vessels of skin ; 

2,2, lymphatic trunks connected with these 

vessels. 



ABSORPTION. 127 

in others, which have an imperfect apparatus for circula- 
tion, it passes through the coats of the intestines, and is 
carried into the bloodvessels by endosmose. In insects the 
fluid is diffused without passing into circulating vessels. 



QU ESTI ONS. 



What is meant by absorption? 

What relation does it bear to digestion ? 

What fluids are absorbed by the blood-vessels of the stomach and 
intestines ? 

What other vessels are found in the intestines? 

What are the lymphatic vessels, and what do they contain? 

How is the absorbing surface of the intestine increased ? 

What are the villi? 

How is absorption through the villi effected? 

Explain the process of endosmose or imbibition. 

What becomes of the chyle after entering the lacteals? 

What little bodies found along these vessels assist in the elaboration 
of that fluid? 

Through what channel does chyle pass to the liver? 

What kinds of materials are absorbed by the chyliferous vessels after 
digestion? 

What action is exerted by the veins of the intestine? 

Where are the lymphatic vessels found ? 

What is their duty, and where is the lymph emptied? 

What arrangement prevents the backward flow of the lymph? 

What other forces assist in the movement of the lymph in the vessels? 

What is the lymphatic heart? 

What is the peculiarity of the lymphatic system in fishes and reptiles? 
In birds? 

What kinds of animals have no lymphatic system ? What then be- 
comes of the digested food? 

What is the arrangement in insects? 



RESPIRATION. 



Object of Respiration. — It has now been shown in what 
way the fluids formed during digestion, and the lymph 
resulting from the general wear and tear of the various 
parts of the body, pass into the general circulation. When, 
however, they empty into the veins they are not in a fit 
condition to nourish the tissues. The blood itself is not 
then perfect; it must be purified and its tone improved. 
To effect such a change upon it it is necessary that it 
should be brought in contact with the air breathed into 
the lungs, and this action begins at the very first moment 
of existence. The mode in which this conversion of venous 
blood into arterial blood is produced is now to be studied 
under the head of Respiration. 

Changes Produced. — Respiration may be defined as the 
function by which venous blood is converted into arterial 
blood. The change takes place in the lungs, the oxygen 
of the air being imparted to the blood and carbonic acid 
being given off. 

To show clearly to the eye that carbonic acid is given off 
from the lungs, the following simple experiment may be 
made : Fill a wineglass with lime-water, and breathe into 
it through a glass tube, when the invisible carbonic acid of 
the breath will at once unite with the lime and soon throw 
down flakes of chalk or carbonate of lime. After obtain- 
ing this deposit, add a little vinegar to it — which has a 
stronger attachment to lime than carbonic acid has — and 

]28 



RESPIRATION. 129 

the carbonic acid will be set free, and be seen effervescing, 
as it is called, or bubbling up. There is also a certain 
amount of watery vapor discharged from the breath. It 
is seen as condensed on a window-pane when breathed 
upon, or on a cold day in the cloudy vapor that is visible 
as it comes from the mouth and nose. 

The process of respiration occurs by a passage of gases 
— oxygen and carbonic acid — through the delicate mem- 
brane of the bloodvessels of the lungs, just as we have 
already seen was the case with fluids in the absorption of 
chyle. It has been found by experiment that even when 
an already moistened membrane will not admit of the pas- 
sage of fluids through it, gases can frequently penetrate them. 
Before the blood reaches the lungs it is called vmous blood, 
because it flows through the veins and is of a dark bluish- 
red color. After it has received oxygen in the lungs the 
color is changed to a bright vermilion, and the blood is 
then called arterial blood, because it is carried in the 
arteries. 

One peculiarity in regard to the act of respiration which 
cannot be stated of the other functions we have considered 
— Digestion and Absorption — is that it cannot be wholly 
suspended or stopped for more than a few moments without 
causing immediate death. Venous blood requires the con- 
version just mentioned, because it is an impure fluid con- 
taining materials that have already served for the support 
of life in various parts of the body. Even the chyle, that 
is to play such an important part in maintaining the gen- 
eral nutrition of the body, must be made more perfect, more 
like the blood itself. 

When we come to study the subject of the Circulation 
we shall be able to appreciate more clearly the manner in 
which the blood passes from the right side of the heart to 



130 PHYSIOLOGY. 

receive its supply of oxygen. For the present we need 
only impress the general fact that such a conversion does 
take place, and defer the consideration of the details as a 
part of the sketch of the general circulation of the blood. 
It may be stated that the subject of respiration includes 
only this passage through the lungs, for when the blood 
leaves the lungs after being aerated it must be considered 
as a portion of the circulation. 

The Chest and its Contents. — Before studying the process 
of respiration, let us first inquire into the nature of the 
organs concerned in it. The lungs are two large marble- 
blue organs, which with the heart fill the whole cavity of 
the chest, and which when once filled with air float in water 
ever afterward, as may be shown with a calf's lung re- 
moved from the animal. The chest, technically called the 
thorax, is a conical bony cage (Fig. 1), covered on the 
outside and lined on the inside with muscles, and separated 
from the abdomen by a large muscle called the diap/iragm, 
which forms the floor of the chest and separates it from 
the abdomen. The diaphragm is so called because it sep- 
arates these two important cavities, in this respect acting 
like a partition or diaphragm anywhere else. The thorax 
is made up of a portion of the spinal column at the back 
part and twelve ribs on each side, passing from the spine 
to or toward the breast-bone (Fig. 1). Seven of the ribs 
are attached to it — not directly, but by the medium of elastic 
material called cartilage, — while the others are either fast- 
ened to one another or float unattached at their front part. 

The ribs are made very movable, so that they can rise 
and fall, and in this way dilate and contract the chest 
during respiration. Muscles pass between the ribs, and by 
their action upon them assist in respiration. Perhaps the 
most important muscle concerned in this process is the 



RESPIRATION. 



131 



diaphragm, which is attached around the base of the chest, 
and when relaxed forms an arch, the middle of which is 
opposite the lower end of the breast-bone. All the muscles 
of the chest and also those of the abdomen take part in 
respiration, and, when breathing is rapid and excited, those 
which raise and lower the ribs are especially called into 
play. 

The Lungs. — The lungs are so arranged as to give a very 




Fig. 49. — Lungs, Heart, and Diaphragm in position. 

1 pulmonary vein: 2, pulmonary artery; 3, main artery from heart; 4, vein; 5, 
carotid artery ; 6, jugular vein ; 7, windpipe ; 8, larnyx ; 9, coronary artery ; A, B, 
V, I), heart; E, F, lungs; G, diaphragm. 

large surface for the contact of the blood and the air, and 
to do this to the best advantage each of the very small 
bloodvessels is completely surrounded by air. The lungs 
are divided into smaller portions, called lobes — the right 



132 



PHYSIOLOGY 



lung into three 
called the plea' 
fleeted over the 
keeps it always 
but get darker 
The air of the 
through the air 



, the left into two. A delicate membrane, 
ra, lines the interior of the chest and is re- 
lungs and heart. It secretes a fluid which 
moist. In infancy the lungs are pale red, 
by age, being in old persons a livid blue, 
external atmosphere is tempered on its way 
-passages, especially by the warm circulating 



Windpipe. 




L. Bronchial 
ube. 



Fig. 50. — Thk Lungs and Bronchial Tubes (the lung-structure on one 
side being supposed to bo removed). 

blood in the lungs, so that when it comes in contact with 
the delicate structures of the latter it produces no injurious 
effect. The air after it enters the mouth passes along the 
throat into the kir'ynx (Fig. 83), which we shall hereafter 
describe as the organ of voice, thence into the windpipe or 
track 'ea (Figs. 49, 50), which divides into two large tubes or 
canals called the broncklal tubes. These tubes divide, one 



RESPIRATION. 



133 



entering 



subdivide 

i 



become 




Fig. 51 — Lobule of Lung (magnified). 

1, small bronchial tube; 2, termination in 
air-cell; 3, pulmonary tissue. 



each lung, and 
very minute and very nu- 
merous, and penetrate 
every part of the struc- 
ture of the lung (Fig. 50), 
leading to minute cavities, 
which terminate at last in 
blind extremities or sacs, 
having very thin walls, and 
called air-cells (Fig. 51). 
These cells are covered 
with a network of very 
minute bloodvessels. The 
air we breathe does not 
therefore circulate in the 
substance of the lungs 
proper, for it cannot get 
beyond the air-cells just mentioned (Fig. 51). These be- 
come distended after a full inspiration of air, and remain 
partially so during life as long as breathing lasts. The 
air-passages in some portions have rings of cartilage (Fig. 
50) to strengthen them and to impart elasticity. The air- 
passages are lined by a mucous membrane, similar to that 
which lines the alimentary canal, and to which reference 
was made in the chapter on Digestion ; and the same kind 
of fluid is poured out to keep the air-tubes moist. On this 
membrane, as seen under the microscope, are numerous 
cells like hairs, to which the name cil'ia (meaning eye- 
lashes) has been given, and they have a waving motion like 
a field of grain, the motion being upward and outward 
toward the mouth. They possibly assist in carrying, in a 
direction away from the lungs, any fine particles of dust, etc. 
that might otherwise pass into the more delicate air-passages. 

12 



134 PHYSIOLOGY. 

The Act of Breathing. — The terms inspiration and ex- 
piration are applied to the filling and emptying of the 
kings in the act of breathing. These are effected by the 
alternate contraction and enlargement of the chest by the 
action of muscles, especially those connected with the ribs. 
When the thorax or chest contracts, expiration occurs, and 
the air is*expelled from the lungs through the various 
tubes already mentioned, and through the mouth and nos- 
trils. Expansion of the chest — that is to say, its enlarge- 
ment in length, width, and height — produces inspiration. 
The process of respiration is partially and but temporarily 
under the control of the will, so far as moving the chest is 
concerned, and it continues without cessation as long as life 
lasts. When expiration has taken place, the need of imme- 
diate inspiration becomes so absolutely felt that it cannot 
be postponed. Swimmers in making a plunge into the 
water cannot long delay their return to the air above to 
complete the act of respiration. There is, however, a slight 
but brief period of repose, which cannot be safely prolonged. 

The alternate expansion and contraction of the thorax 
may be illustrated by a pair of bellows, the nozzle being 
the windpipe, the flexible leather uniting the boards the 
diaphragm, the boards themselves being the ribs, and the 
hinges the attachment of the ribs to the spinal column. 
When the diaphragm is extended, and the ribs elevated by 
the muscles connected with them, the dilated chest has its 
counterpart in the bellows when the boards are separated. 
The air rushes into the nozzle, as it would into the wind- 
pipe, to fill up the vacuum, and the bellows is emptied in 
a similar way to that of expiration. It may be said that 
the lungs are active in inspiration, but in expiration they 
are passive, their only duty being to empty themselves 
gradually by their own elasticity. 



RESPIRATION. 135 

Gentle Respiration. — Gentle, easy respiration in man is 
effected by the elevation and depression of the diaphragm, 
without calling all the other muscles into active play. This 
muscle of course presses upon the contents of the abdomen 
whenever it is depressed in producing enlargement of the 
chest. When the diaphragm is elevated, 
as in expiration, the stomach and intes- 
tines again return to their natural po- 
sition, and this explains the visible 
swelling and contraction of the abdomen 
during respiration. The effect of easy 
respiration by the diaphragm and ab- 
dominal muscles, as well as that of forced 
respiration by the chest, may be seen in 
the illustration (Fig. 52). Such easy res- 
piration is that seen in those who are 
sleeping. In deeper and more active 

i ,i . -, Fig. 52. — Gentle and 

respiration, such as that occurring under ^ 

r 7 to Forced Respiration 

excitement, a large number of other (the latter shown in 
muscles are called into exercise. the dotted lme )- 

Number of Respirations. — As a general rule, the number 
of respirations is eighteen in a minute ; that is to say, there 
are accomplished in this period of time both inspiration 
and expiration, with a very brief period of repose. The 
estimate usually made is that while the heart is making 
four beats in the circulation of the blood one act of res- 
piration is taking place. Of course during exercise and 
motion the number of respirations is increased. Age has 
also a modifying effect ; in the infant the number is con- 
siderably greater than in the adult. A young baby at and 
soon after birth will breathe at least forty times a minute ; 
the child of five years of age will have about twenty-five 
respirations a minute ; and so the number goes on dimin- 




136 PHYSIOLOGY. 

ishing until about the fifteenth or sixteenth year, when the 
number reaches, say, eighteen per minute — characteristic 
of adult life. It may be briefly said that whatever excites 
the individual in any way, especially if it affects the action 
of the heart, increases the activity of respiration, and 
therefore the number of respirations. 

Full Respiration. — A greater amount of muscular effort 
is used than in ordinary easy respiration when we breathe 
rapidly or forcibly. The muscles of the chest, even those 
which are attached to the neck or the arm, are called into 
service so as to enlarge that cavity. The upper part of the 
chest has usually but little motion, unless the breathing be 
rapid, especially in the female. Indeed, woman breathes 
more with the chest, even in gentle, easy respiration, than 
man. This natural tendency is increased by the mode of 
dress, which should, however, be such as not to compress 
the walls of the chest or to interfere with the free motion 
of the ribs. It has been shown by experiment that in 
easy inspiration the larynx, the organ of the voice, is not 
movable, and there being perfect absence of fatigue, sing- 
ing can be prolonged for a greater length of time. When 
the upper ribs are rapidly raised, as in forced respiration, 
general and vocal fatigue ensue very rapidly, for the organ 
of voice can no longer depend on the assistance of sur- 
rounding muscles, but must call into play all its own 
muscular power. 

Sounds of the Chest. — In applying the ear to the chest 
a gentle sound is heard, caused by the penetration of air 
into the air-cells. This sound, as well as that louder and 
rougher sound caused by the passage of air along the 
various tubes, is changed in its character by disease of 
those parts ; and the physician, who is familiar with the 
natural, healthy sounds in breathing, soon recognizes the 



RESPIRATION. 137 

differences noticeable in them when so affected by inflam- 
mation or other diseased condition. He can also learn by 
striking over the chest with his finger whether the air-cells 
are doing their proper duty, for the sound will then be 
clear, as it will always be in sounding over a cavity filled 
with air. If the cells do not contain air, but have become 
solid or obstructed from any cause, the sound will not be 
any longer clear, but dull and obscured. 

Capacity of the Lungs. — When air enters the air-cells 
of the lungs it is not wholly expelled in expiration. A 
certain quantity always remains behind, and this is called 
the reserve air. It is hardly, therefore, correct to speak of 
emptying the lungs in the act of expiration. When the 
lungs are fully expanded by the air, the quantity has been 
estimated at rather more than three hundred cubic inches, 
or more than four quarts. The average quantity breathed 
out at each expiration is estimated at about twenty cubic 
inches, so that rather less than three hundred cubic inches 
remain behind after each expiration. The entire air in 
the lungs is therefore thoroughly renewed about once in 
a minute. In easy respiration the whole amount of the 
breathing capacity of the lungs is not called into play. 
Estimating the quantity of air breathed per minute at 
three hundred and sixty cubic inches, or about ten pints, 
an idea may be formed of the immense quantity breathed 
in the course of twenty-four hours. 

The Air-Ceils. — To give some idea of the size of the air- 
cells, it may be stated that the smallest bronchial tubes — 
capillary tubes they are called, because they are almost 
hair-like in their dimensions — measure from the fiftieth 
to the thirtieth of an inch, the air-cells from the two- 
hundredth to the seventieth part of an inch. A thick net- 
work of delicate and minute bloodvessels covers the walls 

12* 



138 PHYSIOLOGY. 

of the air-cells and the passages between the cells. These 
communicate on one side with the arteries in the lungs, 
called the pulmonary arteries (from pulmo, "a lung"), on 
the other with the pulmonary veins ; and here the change 
from venous to arterial blood takes place, the pulmonary 
veins carrying the purified blood to the left side of the 
heart (Fig. 152). 

The Air we Breathe. — Pure atmospheric air is composed 
of two gaseous substances, called nitrogen and oxygen, 
mixed together in the proportion of 79 parts of nitrogen 
to 21 parts of oxygen, or, in round terms, one part of 
oxygen to four of nitrogen. It contains in addition a 
small quantity of watery vapor and a very minute quan- 
tity of carbonic acid — only one part in 2000 parts of the 
atmosphere — scarcely sufficient to take note of. Oxygen 
alone would be too stimulating, and life would be main- 
tained at such a higli pressure, so far as respiration is con- 
cerned, that death would soon occur from over-stimulation. 
Diluted with the nitrogen, however, it is a powerful and 
energetic agent for respiratory purposes. The amount of 
carbonic acid in the air under ordinary circumstances is not 
sufficient to do any harm, but when it becomes increased in 
quantity, as we shall hereafter see, very serious effects ensue. 
When the air is examined after it has been breathed out of 
the lungs, it is found to contain a much smaller amount of 
oxygen than when it was inhaled, and a greatly increased 
quantity of carbonic acid. This shows that oxygen has 
been absorbed into the lungs and carbonic acid given oil* 
from them. A small amount of watery vapor is also 
exhaled from the lungs at each inspiration. 

It will be seen hereafter that the blood contains numerous 
little structures, called corp'uxcles (signifying " little bodies," 
from corpus, " a body "), visible only under the microscope. 



RESPIRATION. 130 

These are the parts of the blood that are acted upon by the 
oxygen taken into the lungs at an inspiration. 

Mechanical Actions in Breathing. — A variety of mechani- 
cal actions are connected with the function of respiration. 
The exercise of the voice is an illustration, whether used in 
speaking or singing. Coughing, sneezing, laughing, smell- 
ing, sobbing, spitting, yawning, snoring, etc. are all modified 
forms of inspiration or expiration, or of both combined. 

Sighing is a deep inspiration, by which air is slowly in- 
haled in large quantities, frequently because, through lan- 
guor or emotion, the blood does not receive a sufficient 
amount of pure air, or, in other words, is not properly 
aerated in the lungs. The process of respiration may be- 
come sluggish and irregular if the mind is wholly absorbed 
by any cause diverting the attention from it, such as attends 
the preoccupation of the mind, as by literary labor, emotion 
in some form, etc. The blood does not then become per- 
fectly aerated, and the poor venous blood does not undergo 
properly the change into the richer arterial blood. It is 
then that a long sigh or series of sighs comes to our aid, 
and rapidly supplies the amount of air necessary to give 
to the blood the oxygen it requires. 

Coughing is a violent action of the muscles of expiration 
and contraction of the muscular fibres of the bronchial tubes. 
Laughter is a convulsive action of the muscles of respiration 
— including the diaphragm — and of the voice, combined 
with action of the muscles of expression of the face. Yawn- 
ing is a deep inspiration, attended with contraction of the 
muscles of the lower jaw and part of the throat. Sobbing is 
similar in its causes to laughter. Panting is a series of 
short, quick inspirations and expirations, and seems to have 
for its object the rapid renewal of air in the lungs in cases 
in which the circulation is too rapid or where an extra 



140 PHYSIOLOGY. 

supply of fresh air is demanded. Smelling is a series of 
short inspirations while the mouth is shut, so that the whole 
impression of the odor may be made upon the cavities of 
the nose alone. Sneezing is a violent expiration, in which 
the air, rapidly driven from the chest, agitates the cavities 
of the nose with a peculiar but familiar sound. 

Obstacles to Respiration. — We have already said that the 
danger to life is great and immediate if the respiration be 
suspended for a few moments. This may occur from va- 
rious causes, such as from strangulation, from drowning, 
from hanging, from pressure on the chest interfering with 
its movements, etc. ; but whatever the exciting cause may 
be, the effect is always the same — the non-conversion of 
venous into arterial blood, the necessary oxygen not being 
received. This condition of the lungs may result from ab- 
sence or insufficiency of the pure air that the lungs are in 
the habit of inhaling ; from the presence in the air of some 
other gas instead of oxygen, etc. Air once breathed is un- 
fitted for further respiration, being no longer pure. The 
amount of oxygen in it is found to be greatly lessened. 

If too many persons are crowded together in a room the 
atmosphere becomes more and more vitiated by the breath- 
ing out of so much carbonic acid from so many lungs, and 
the effect on each individual soon becomes apparent, for 
carbonic acid is what is called an irrespirable or unbreath- 
able gas. To ensure perfect respiration the air that is 
breathed must be renewed, and not allowed to be contami- 
nated. One of the most familiar and frequently quoted 
illustrations of the effect of confinement in a close atmo- 
sphere is that of the " Black Hole of Calcutta," as it is 
generally known. In a war between the English and the 
people of a portion of India in the eighteenth century, 146 
of the former were captured and imprisoned in a small 



RESPIRATION. 141 

room only twenty feet square, into which but little light 
and air penetrated, and the heat was intense. The next 
morning, after a night of dreadful suffering and an interval 
of only eight hours, all except twenty-three of the pris- 
oners so confined were found to have died. 

Death is not due alone to the additional amount of 
impurity given to the atmosphere under the circumstances 
just named ; there is also a certain amount of animal 
or organic matter exhaled from the lungs of man and all 
other animals which rapidly putrefies and poisons the at- 
mosphere. Amid all the comforts of modern homes danger 
to health or life may ensue from the very conveniences 
which surround their inmates; a burning gaslight in a closed 
room at night will evolve far more carbonic acid than would 
be given off from the lungs, and burning fires in stoves 
and heaters may be perpetually poisoning the air. 

Ventilation. — It will be at once seen, after these allusions 
to the ill effects of impurities in the atmosphere, how ne- 
cessary it is to adopt all proper means of prevention, so 
that the air of rooms occupied at the same time by a number 
of persons can be properly changed and kept pure. Schools, 
assembly-rooms, hospitals, etc. should have doors and win- 
dows and chimneys so adjusted that such a result can be 
perfectly accomplished, and that all mental effort, in schools 
especially, should not be hampered by deficiency of atten- 
tion to the true principles of the physiology of respiration. 
It is not necessary to go into the details of the best form 
of construction of buildings to ensure perfect ventilation. 
Let it be remembered that the first and most important 
object is to give an outlet to the impure air, which as it 
becomes warm will rise, and an inlet to the pure external 
air ; that cold air is not any purer than warm ; and that 
it is not necessary to create a draught, a gentle current 



142 PHYSIOLOGY. 

being all that is required. Perhaps one of the best modes 
of ventilation is the open fireplace, which creates a draught 
up the chimney and carries off impurities through that 
channel. 

Summary. — We may briefly sum up our knowledge of 
the process of respiration in man as follows : The air when 
breathed loses some of its oxygen, but acquires carbonic 
acid. The blood undergoes a change in color, which is 
undoubtedly caused by contact with oxygen. The blood in 
the lungs loses some of its carbonic acid. The oxygen of 
the inspired air passes directly through the coats of the 
vessels of the lungs. Aqueous vapor is also discharged 
from the lungs. 

Respiration in Animals generally. — The process of respi- 
ration in other animals than man has its peculiarities, the 
lungs of birds, fishes, and insects differing greatly. The 
process is similar to that of man, so far as the interchange 
of gases is concerned between the blood and the atmosphere, 
oxygen being taken in and carbonic acid given off. In the 
lowest forms of animal life this takes place without the 
presence of lungs, the whole external surface acting as a 
medium for this purpose. In such a case the atmospheric 
air penetrates their tissues and exerts its action upon the 
fluids contained in them. In animals which have a thick 
or hairy skin or hide this would be impossible, and their 
lungs are usually sufficiently developed to carry on the pro- 
cess of respiration. 

In birds the lungs are quite small and attached to the 
chest. The pleura covers them on the under surface; only. 
A considerable part of the chest and also of the abdomen 
is occupied by membranous air-cells, with large openings 
communicating with the lungs (Fig. 53). In some birds the 
bones also form receptacles for the air, the object being to 



RESPIRATION. 



143 



make the body so light that flight will be easy. Those 
which fly most rapidly and to the greatest heights — the 
eagle, for example — have these bony cells in the largest 
number. The air thus supplied enables the bird to fly and 
sing without the necessity of taking breath constantly. The 



Trachea 



Tulmonary vessels 

Lung. 

Bronchial openings 




Bronchia open. 



Bronchia open. 



Fig. 53. — Lungs of a Bird. 

air seems to penetrate usually into bones which are intended 
for locomotion, as in the ostrich. 

Respiration in fishes is performed by gills (technically 
called branch' ice), membranes largely supplied with blood, 
placed behind the head on each side, to which is attached a 
movable gill-cover. Generally there are four gills on each 
side. The fish does not breathe the air of the atmosphere, 
but the air contained in the water in which it swims. The 
water passes into the throat, and is conveyed to the gills, 
through which it passes, making its way through the open- 
ings. Water is richer than the atmosphere in oxygen. 
Some fish, however, do not derive a sufficient amount of 
oxygen from the water, and rise occasionally to the surface 
for a larger supply. 



144 



PHYSIOLOGY. 



Reptiles have feeble respiratory action ; some have lungs ; 
some early in life have gills ; others are supplied with both 
lungs and gills. These last can live both on land and in 
water, and in some of them the whole surface of the body 
is an active medium for respiration and the interchange of 
gases. The lungs of reptiles receive air that is swallowed 
rather than breathed, and are generally made up of air- 
sacs divided by partitions. 

In insects, respiration is usually effected through the 






Fig. 54. — Respiration' ix Insects illustrated. 

A, stigmata, or respiratory orifices, of water-beetle ; B, a single opening, greatly 
enlarged ; C, trachea. 

exterior of the body. In them the air enters through 
openings (technically called dig'mata) ■ which are the ter- 
minations of air-tubes, or tracheae, and convey the air to 
all parts of the system. In all cases, however, there is the 
same kind of interchange of gases in animals generally that 
lias been described as the chief feature of respiration in 
man. 

Respiration in the Vegetable. — There is a genuine process 
of respiration in the vegetable as in the animal, but of a 



RESPIRATION. 145 

different and peculiar kind. It is indeed a reversal of all 
that we have said in regard to the animal, for while the 
latter absorbs oxygen and gives off carbonic acid, vege- 
tables, under the influence of light, absorb carbonic acid 
and give off oxygen, the carbon becoming a part of the 
substance of the plant. Under other conditions oxygen is 
absorbed and carbonic acid gotten rid of by them, so that 
at night plants are unsafe companions in a sleeping-room. 
All those portions of the plant which are not green — and 
this applies to the flowers especially — absorb oxygen and 
give off carbonic acid, whether we examine them in the 
light of the sun or in the shade. Ripe fruit, it is said, 
respires in the same way, and grain that is germinating 
under the influence of air and moisture also has a similar 
interchange of gases. It may be stated, then, in brief, that 
the main difference between animals and vegetables, so far 
as respiration is concerned, is the fact that animals always 
absorb or take in oxygen, while vegetables do so only under 
certain conditions of their life. 



QUESTIONS 



What change is necessary to purify the venous blood? 
In what organ does the change take place? 

What is the function called under which this conversion takes place? 
What is the definition of Respiration? 
What gases are concerned in the process? 
Which is absorbed ? Which is given off? 

By what simple experiment can it be proven to the eye that carbonic 
acid is given off? 

What gas is given off when a liquid effervesces? 
What vapor is given off from the lungs, and when is it visible? 
How is the passage of the two gases effected in the lungs? 
Do gases or liquids penetrate moist membranes most readily? 
13 K 



146 PHYSIOLOGY. 

What changes take place in the color of the blood during respiration ? 

Can respiration, like digestion, be suspended ? 

Why does venous blood require conversion? 

What part of the circulation is concerned in the function of respira- 
tion? 

What organs are the chief agents in respiration ? 

What organs fill up the cavity of the chest? 

What is the thorax ? How is it covered ? 

What muscle separates the chest from the abdomen ? 

How are the ribs arranged ? How are they moved ? 

What other muscles take part in respiration? 

What is the relation of bloodvessels to the air- tubes? 

What is the pleura ? 

How does the color of the lungs vary at different periods of life? 

How is the cold air tempered in breathing? 

W 7 hat is the course of the air when breathed? 

What is the arrangement of the larger and smaller bronchial tubes? 

What are the air-cells ? 

What two processes does the act of breathing include? 

How is each affected by the motion of the ribs and the muscles? 

What effect has expansion or contraction of the chest on inspiration 
or expiration ? 

How can the act of respiration be illustrated by the action of the 
bellows ? 

Are the lungs active in inspiration or expiration? 

How is gentle, easy respiration effected ? 

What is the action of the diaphragm ? 

What is the number of respirations per minute? 

How does this compare with the number of beats of the heart? 

How does age affect the number of respirations? 

What effect does excitement have upon them ? 

What other muscles are called into use in violent respiration ? 

How does the breathing of woman differ from that of man? 

How is the voice affected by easy or rapid breathing? 

What are the sounds of the chest in respiration ? 

What information do they afford the physician ? 

Are the lungs emptied when air is taken into them ? 

What is the breathing capacity of the lungs? 

What is the average quantity breathed out at each expiration ? 

How often is the air in the lungs renewed? 

What is the size of the smallest bronchial tubes? 



RESPIRATION. 147 

What is the size of the air-cells? 

What are the smallest bronchial tubes called? 

What is the relation of the bloodvessels to the air-cells. 

What are the main bloodvessels of the lungs called? 

Of what materials is the atmosphere composed ? In what proportions? 

What vapor does the air contain ? 

How much carbonic acid is present in the atmosphere? 

Why would not an atmosphere of oxygen alone do for respiratory 
purposes ? 

What little bodies exist in the blood ? 

What parts of the circulating blood are acted upon by the oxygen ? 

Mention some of the mechanical actions which are connected with the 
process of respiration. 

What is sighing? In what conditions may it be beneficial? 

Explain the respiratory actions involved in coughing; in laughing; 
in yawning; in sobbing; in panting; in sneezing; in smelling. 

From what causes may respiration be suspended? 

What is the effect of such suspension on the purification of the blood? 

What is the effect of crowding persons together? With what gas is 
the air then contaminated ? 

What animal matter is given off from the lungs? 

Sum up the general facts of the process of respiration. 

How does respiration in animals resemble that of man? 

Are lungs always present? 

What is the arrangement of the organs of respiration in birds? How 
do the bones aid in the process? 

What is the peculiarity of the respiration of fishes? 

Which contains the most oxygen — air or water? 

How is respiration effected in reptiles? In insects? 

What are the stigmata of insects? 

How does respiration in the vegetable differ from that of the animal? 

In what points do they resemble one another? 

Why should plants not be kept in bedrooms at night? 



CIRCULATION. 



Object of the Circulation. — As the blood is the great 
medium through which all parts of the body are nourished, 
it becomes necessary that an apparatus should exist by 
which it may be distributed everywhere. We have already 
seen how blood was formed from the food aud from the 
lymph as a result of the processes of Digestion and Ab- 
sorption, and how, by the process of Respiration, it is 
purified in the lungs so as to be fitted for the nourish- 
ment of the body. Under the head of the Circulation we 
are now to study the manner in which it is to be transmitted 
to the various organs. In studying the course of the circu- 
lation we shall see that the purified blood, after leaving 
the lungs, passes directly to the left side of the heart. The 
heart is the great central organ of its distribution, and 
sends the aerated blood out upon its travels, to receive it 
once more after it has gone its rounds and performed its 
duty. The process is called Circulation, because the pas- 
sage of blood from the heart all through the body and back 
to the heart through the bloodvessels is like a movement 
in a circle. The discovery of the plan of the circulation of 
the blood is due to a physician named William Harvey 
of London, England, who early in the seventeenth century 
demonstrated its existence. 

The Heart. — The heart (Fig. 56) is chiefly a muscular 
organ, with wonderful contractile powers. It is in shape 
somewhat like a cone, and lies in the middle and front 
part of the chest, a little to the left (Fig. 55), between the 

1-18 



CIRCULATION. 



149 



hings (Fig. 49). It weighs usually about ten or twelve 
ounces, being, it is said, about the size of the fist, although 
this is a variable measurement. It is five inches long, 
three and a half wide, and two and a half thick. It is 
lined by. a thin membrane, called the endocardium (from 
two Greek words meaning " within the heart "), and cov- 




\ \ 



\<3J 

Fig. 55. — The Hkart in its Natural Position 7 in the Chest. 

a, b, c, </, e, ribs; 1, 2, 3, 4, 5, spaces between the ribs covered with muscles. (The 

vertical line represents the middle line of the body.) 



ered by another called the pericar'dium (from two Greek 
words meaning " around the heart"). The heart is a red 
muscular mass, a familiar counterpart of which is seen 
in the bullock's heart on the butcher's stall. 

The Heart a Double Organ. — The heart in man consists 
of four compartments or cavities, two of which receive the 

13* 



150 



PHYSIOLOGY. 



blood and two propel it. The heart is really a double 
organ, having two distinct portions with their cavities. 
The right side, or right heart, as it might be called, re- 
ceives the dark venous blood from the system generally, 




Fig. 56. — The Heart, Exterior View. 
1, right ventricle; 2, left ventricle; 3, right auricle; 4, left auricle; 5, aorta; 6, pul- 
monary artery; 7, 8, 9, large arteries branching oft" from aorta; 10, vena cava; 
11, pulmonary veins. 

and sends it to the lungs to be converted into red arterial 
blood. The left side, or left heart, receives the blood from 
the lungs, and sends it out everywhere through the body. 

Cavities of the Heart. — Each side has two cavities, called 
an aur'icle (" a small ear ") and a ven'tricle (literally, " a 
little stomach"), (Figs. 56-59). There is no direct communi- 
cation between the right and the left heart except through the 



CIRCULATION. 



151 



lungs. The right auricle 
receives the blood, and 
sends it into the right 
ventricle, which forwards 
it to the lungs. The left 
auricle receives the blood 
from the lungs, and the 
left ventricle propels it 
into large vessels, called 
arteries, to be distributed. 
As a rule almost without 
exception, the vessels that 
carry blood to the heart 
are called the veins; those 
which carry it in an oppo- 
site direction the arteries. 
The left side of the heart, 
having a greater amount 
of work to perform in the 
propelling of the blood 
through the whole sys- 
tem, has much thicker 
walls than the right side. 
The muscular walls of 
the ventricles on both 
sides are thicker than 
those of the auricles, as 
the duty of the former 
is to propel to a greater 
distance. 

The Greater and Lesser 
Circulation. — The right 
heart, from its containing 




Fig. 57. — The Heart and its Cavities. 
(Showing lesser and greater circulations.) 
of, right auricle; b, right, ventricle, communi- 
cating through auriculo-ventrieular opening; 
c, pulmonary artery, showing branches to each 
lung; d, capillary vessels of lesser or pulmonic 
circulation ; e, pulmonary veins ;/, left auricle, 
and g, left ventricle, communicating through 
left auriculo-ventrieular opening; h, aorta; 
i, arteries ; k, upper vena cava, bringing blood 
from upper portions of body to right auricle; 
I, arch of aorta; m, its descending portion; 
n, arteries of stomach and intestines; o, capil- 
laries of intestines ; p, portal canal ; g, capil- 
laries of portal system in liver; r, veins of 
liver; .?, lower vena cava, bringing blood to 
right auricle from abdompn and lower por- 
tions of body ; t, capillaries of greater or sys- 
temic circulation. 



152 



PHYSIOLOGY. 



venous blood, is sometimes called the ve/nous heart, or the 
pul'monary heart because it carries the blood to the lungs. 
The left side is called also the arte' rial heart, because it 
contains arterial blood ; the aor'tic heart, because it sends 
the blood directly into a large vessel called the aor'ta, the 
largest artery in the body ; or the system' ic heart, because 
it distributes the blood to the system generally. This ar- 
rangement of the heart 
establishes two circula- 
tions instead of a single 
one. One of these is 
from the right side of 
the heart, through the 
lungs to tiie left side, 
and is known as the 
lesser or pulmonic cir- 
culation; the other is 
that formed by the cir- 
cuit of the blood all 
through the body from 
the left side of the heart, 
through the arteries and 
. back bv the veins, to the 

1, right ventricle •?, left ventricle; 3, right aun- * # 

cle: 4, left auricle: 5, opening between right right side of the heart, 

auricle and ventricle-tricuspid valve ; 6 open- d . ^ ^ ^ 

ing between left auricle and ventricle ; /, pul- «' 

inonary artery and semilunar valves ; 8, origin or* SVStem' iC CI I'Cldatioil 

of the aorta with its valves; 9, 10, opening of , j^. p:*\ Tl 1 * 

venae cava? into heart; 11, openings of pul- \^ *&• Of J. 1 J1C ODjeCL 

monary veins. f the smaller circula- 

tion, as already shown, is to reconstruct and purify the blood 
by aeration in the lungs; that of the greater circulation is 
the nourishment of the various organs. 

Valves of the Heart (Fig 58). — The opening between the 
right auricle and right ventricle is guarded by a valve called, 




Fig. 58. — Interior of thk Heart. 



CIRCULATION. 



153 



from its shape, the tricuspid valve (because it has three 
cusps or points), and that between the left auricle and left 
ventricle by the mi'tral valve, from its fancied resemblance 
to a bishop's mitre. These valves are intended to pre- 
vent the reflow of blood, so that the circulation shall be 
continuous. As the blood cannot flow backward when 
these valves are closed, it must go forward when the 




Fig. 59. — General View of the Heart and Great Vessels proceeding 

from IT. 
a, a', venae cavge : b, right auricle ; c, right ventricle : d, d', pulmonary arteries; e, e', 

pulmonary veins;/, left auricle; g, left ventricle; h, k', It'', h"', main aiteries 

branching off from the aorta. 

heart contracts upon its cavities. There are half-moon- 
shaped valves also, called therefore semilunar, both at the 
mouth of the pulmonary artery — a vessel which carries the 
blood from the right ventricle to the lungs — and at the 



154 PHYSIOLOGY. 

origin of the aorta, or main artery of the body, from the 
left ventricle. 

Movements of the Heart. — The movements of the heart 
are rhythmical; that is, in a regular succession of con- 
tractions and relaxations. When the heart contracts the 
act is called the sys'tole (a Greek word meaning "contrac- 
tion"), the relaxation or dilatation being known as the 
dias'tole (a Greek word meaning "dilatation"). The two 
auricles contract and dilate simultaneously, and the two 
ventricles undergo similar movements together ; that is to 
say, there is contraction and dilatation of the auricles, suc- 
ceeded by contraction and dilatation of the ventricles. There 
is a short period, too, of complete relaxation or repose, as 
if the heart was taking a momentary rest before entering 
again on its duty. 

The beat of the heart is felt between the fifth and sixth 
ribs, near the breast-bone. The lower part of the heart is 
called the apex, and is more movable than the upper part 
or base, which is so attached as to be held firmly in place. 
The position of the heart in the chest is well shown in 
Fig. 55. The very smooth membrane covering the heart 
being in two layers, the heart moves between them without 
friction. A small amount of fluid is poured out on this 
membrane to lubricate it. When the heart contracts it 
alters its shape, and has a gliding motion against the walls 
of the chest, to which the term impulse or .shock has been 
applied. 

The movements of the heart are entirely beyond the 
power of the will, although the muscles which make it up 
appear to be like those which in other parts of the body 
are under voluntary control. When the heart contracts it 
sends out all the blood it contains, and when it dilates it 
fills again with that fluid. 






CIRCULATION. 155 

Vitality of the Heart. — The heart possesses a permanent 
power of contractility, which goes on through a long series 
of years without interruption. Although sometimes scarcely 
perceptible — after drowning, for example — the action of the 
heart may sometimes be restored by proper efforts at resus- 
citation. It is well worth while, therefore, under such cir- 
cumstances to persevere for a length of time in our efforts 
to restore life ; although there may be at first but a slight 
spark of vitality on which to build hopes of success. In 
some of the cold-blooded animals, the temperature of whose 
bodies is much below that of man, the heart will continue 
to beat for many hours or even days after its removal from 
the body. This is seen in the turtle, in some of the ser- 
pents, and in the alligator. 

Sounds of the Heart. — When the ear is applied over the 
region of the heart, two sounds are heard — one, louder than 
the other, over the apex, the other over the base. The 
words lupp, dupp express the sounds heard. The first 
sound is also longer than the second. It is not certain 
whether this first sound is due to the closing of the valves, 
the movement of the blood through the openings, or the 
muscular contraction of the ventricles. It is not due to 
the shock of the heart against the chest, as it is heard in 
the heart of the dog after its removal from the body. The 
second sound seems to be connected with the closure of the 
semilunar valves. In its passage through the heart the 
blood takes the following course : The venous blood, when 
it comes back by the veins to the right side of the heart, 
enters the right auricle, which dilates and fills ; the auricle 
then contracts and fills the right ventricle. This in turn 
contracts and sends the blood Avith some force into the pul- 
monary artery, which carries it to the lungs to be purified. 

After being aerated in the lungs the arterial blood re- 



156 PHYSIOLOGY. 

turns to the left side of the heart, entering the left auricle. 
This cavity then contracts and sends the blood into the left 
ventricle, which by its contraction forces the blood into the 
arteries to be distributed through the body, and back by 
the veins to the right auricle, as before. The valves open 
freely so as to allow the blood to enter, but immediately 
close to prevent a reflow. 

The Pulse. — The series of alternate contractions and 
dilatations is called the beat of the heart. When felt at 
the wrist or at any other superficial part of the body, as at 
the temple, it is called the pulse. *These beats number in a 
healthy grown person an average of about seventy-two to 
the minute. The pulse is increased by food, by exercise, by 
heat, by rising from a horizontal to a vertical position, etc. 
Standing increases the number, giving the heart more 
labor to perform to send the blood to the head, etc., while 
lying down diminishes them. Fasting also diminishes 
them. The number of pulsations per minute — in other 
words, the frequency of beat of the heart — has relation to 
the quantity of blood in circulation. Thus we find the 
following facts in regard to the pulses of different animals : 

Quant it v of Blood XT . r 

Vriodo grammes Nations 

(= 15,000 grains). Pulsations. 

Horse 152 55 

Man 207 72 

Dog 272 96 

Rabbit 020 220 

Guinea-pig 892 320 

It will be noticed in this table that there is a steady 
increase of the number of beats in proportion to the 
amount of blood. 

The effect of emotion on the frequency of beat of the 
heart is well known. Under unforeseen excitement it will 



CIRCULATION. 157 

beat violently, giving rise to palpitation. Sometimes under 
depressing influences, as grief or fear, the action of the 
heart may be so interfered with as to cause fainting, or 
even death from total suspension of its movements. These 
are illustrations of the effect of the nervous system on 
vital organs. The pulse may be naturally much slower or 
faster than the seventy-two beats mentioned as the average. 
Cases have been known in which through a lifetime the 
pulse has been as low as sixty, or even less, to the minute. 

At birth the pulse of the infant is as high as one hun- 
dred and forty beats a minute, and during the early years 
of childhood it is much more rapid than in the adult. It 
again gains a few beats in old age. The pulse of the 
female is somewhat more rapid than that of the male — 
about ten beats faster — although the heart is in size slightly 
smaller. 

The following is a near estimate of the average number 
of heart-beats at different ages : 



At birth 140 

Infancv 120 



Youth 90 

Adult age 72 



Childhood 100 | Extreme old age 75 to 80 

The Heart's Life-Work. — The immense amount of me- 
chanical work done by the heart during a lifetime mav be 
estimated by the number of beats or pulsations, which, as 
we have said, indicates the number of times its cavities 
contract and dilate. Taking the number of pulsations as 
72 to the minute, the following results are obtained : The 
heart beats 4320 times an hour, 103,680 times a day, or 
nearly 38,000,000 times a year. The new-born baby, with 
its numerous heart-beats per minute, in the first year of its 
life accomplishes more than 70,000,000 pulsations. During 
a lifetime of fifty years the heart will have beaten, at the 
least calculation, two thousand million times. Is it not 
u 



158 PHYSIOLOGY. 

remarkable that this small organ, apparently left in charge 
of its own work, should be capable of such continuous and 
unceasing labor? 

The Heart's Repose. — The only rest the heart gets is 
that momentary lull or repose which takes place after the 
second sound of the heart. This period seems to be of 
itself but slight and momentary, and yet at the end of the 
day, if we carefully calculate the amount, we find that the 
heart has had many hours of rest from labor. It has 
been estimated, indeed, that during twenty-four hours the 
ventricles work twelve hours and rest twelve, and the 
auricles work six and rest eighteen. 

The Quantity of Blood. — If Ave estimate the quantity of 
blood sent out by the ventricles at each pulsation at four 
and a half ounces, the amount propelled from it during 
seventy-two pulsations, equivalent to a minute, would be 
324 ounces, or about 20 pounds, being 1200 pounds an 
hour or nearly 13 tons a day. In all these estimates we 
seem to speak of the heart as if it were merely a self-sus- 
taining machine, forgetting, apparently, for the moment, 
that its vital powers are inherent in it, and cannot be ab- 
solutely explained on the principles of any mere mechanical 
apparatus of human construction. 

The whole quantity of blood in the body has been esti- 
mated as being in man T Vj of the weight of the body ; in 
the dog, y 1 ^ ; in the cat, -^ ; in birds, -^ ; in fishes, -g^. 

The Arteries. — When the blood passes from the right 
ventricle into the pulmonary artery, or from the left ven- 
tricle into the aorta — the largest artery in the body — it is 
prevented, as already stated, in each case from flowing 
backward by valves, called from their shape semilunar 
(" half-moon "), which come together and completely shut 
up the cavity (Fig. 58, 7, s). Here begins, at the aorta, the 



CIRCULATION. 



159 




system of vessels called the arteries, which, dividing and 
subdividing, carry the blood which has been purified in 
the lungs, everywhere throughout the body for purposes of 
nutrition (Fig. 60). 

The arteries are solid elastic tubes composed of three 
different coats, the middle one of which is muscular and 
elastic in the larger vessels, and decidedly 
muscular in the minuter arteries. It was 
supposed by the ancients, in their ignorance 
of the nature of the circulation, that they 
contained air ; hence their name (from two 
Greek words meaning " to contain air "). 
The arteries are of a tough structure, to 
bear the heavy pressure of the blood when 
sent into them by the force of the heart, 
and are lined by a very smooth membrane, 
so that the circulation may go on evenly 
and without interruption through the elas- 
ticity and contraction of these vessels. Af- 
ter death they are always found empty, the 
blood accumulating in the venous system. 

The arteries divide and subdivide until at last the mi- 
nutest vessels are only perceptible by means of a microscope, 
and so numerous are the branches sent out that there is 
hardly a portion of the body that is not thoroughly per- 
meated with them. The beat of the heart, communicated 
to the arteries, which constitutes the pulse, is felt at the 
radial artery at the wrist only because the artery is there 
near the surface. By a wise arrangement, almost all the 
other large arteries are more deeply seated, beyond the risk 
of injury, protected by muscles, bones, etc. The pulse is 
felt by the physician chiefly that he may learn something 
of the force and frequency of the heart's action, and its reg- 




Fig. 60.— An Ar- 
tery. 



160 



PHYSIOLOGY. 



ularity and fulness, for these are guides to his knowledge 
of the healthy condition of the individual, the heart being 
itself affected or moved by sympathy with diseased con- 
ditions existing in other organs. 

Pulse-Writing. — An instrument, called a sphyg'mograph 
(from two Greek words signifying " pulse-writer "), has 
been devised, so that the pulse can write on paper the 1 in ^ 
of its own travel. It is a long lever, moved by a screw 
acting on a small horizontal wheel, the point of the screw 
resting on a flat disk of ivory which rests on the pulse. 



Fig. 61. — Tracing of the Pulse at the Wrist in Health. 

The movement of the lever, carried along by clockwork 
over a blackened surface, gives the tracing (Fig. 61). Of 
course in disease the regularity and direction of this line 
would be varied, and the study of the causes of the varia- 
tion would give the physician much information for his 
guidance. When the ventricles contract the vertical line 



Fig. 62. — Tracing of the Pulse at the Wrist in Disease, showing a 
Double Beat. 



is recorded, and when they dilate they produce the wavy 
line. The effect of disease on the pulse is shown in one of 
its forms in Fig. 62, in which the tracing exhibits a double 
beat, an indication to the physician of serious mischief. 
The Veins. — After the blood in the arteries has gone its 



CIRCULATION. 



161 



rounds by those vessels it returns to the heart by the veins. 
These are thinner and less elastic vessels, but are capable 
of distension. In health there is no pulse in a vein, and 
the blood flows continuously and not by pulsatile move- 
ment. When an artery is cut the blood flows from it in 
jets or spurts, on account of the great contractility of its 
coats; but not so with a vein, from which the blood "wells 
out " in a stream. When pulsation is felt in a vein it is 
probably due to obstruction of the circulation in the heart. 
The veins are minute at their origin in the different organs 
of the body, and gradually unite to form larger vessels, 
which communicate with each other, until they at last 
empty into the right auricle by two large trunks, the vence 
cavce, or hollow veins — one into the upper part of the 
auricle, the other (Fig. 57, a,*) into the lower. 

Valves of the Veins. — The veins differ 
from the arteries in another important par- 
ticular. They have valves (Fig. 63), or small 
membranous folds, arranged in such a w T ay 
that they open to receive blood flowing in 
the direction of the heart, and become closed 
to prevent a return of the current in the 
opposite direction. They are more numer- 
ous where the blood proceeds against its 
gravity or Avhere the parts around give 
them a feeble support. They are wanting 
in some of the important organs, such as 
the brain and the lungs. 

The veins are generally nearer the surface 
than the arteries, and contain a darker fluid. 
The safety accorded by nature to the arteries by placing 
them out of the way of injury in secluded places seems 
almost like an indication of intentional protection, by 
14* L 



Fig. 63.— Valves 
of a Vein. 



162 PHYSIOLOGY. 

which no harm shall result to the pure arterial blood in 
its duty of supplying nourishment to the body. 

The Capillaries (from capil'lus, a hair, "hair-like"). — 
These are a system of very minute vessels, visible only 
under the microscope, and intermediate between the arte- 
ries and the veins. It is through the circulation in these 
vessels, which enter into the structure of every part of the 
body, that the nutrition of organs is effected. This capil- 
lary circulation may be seen under the microscope in trans- 
parent membranes, such as the web of a frog's foot, the 
wing of a bat, etc., in which Ave can trace the arteries and 
the capillary vessels coming off from them, finally merging 
into the veins. The more active or important an organ is, 
the richer it is in capillaries. The muscles, for instance, 
which are intended for constant movement, are fully sup- 
plied, while cartilages, whose action is more quiescent, are 
devoid of them. The capillaries are arranged in such a 
way as to be adapted to the organs in which they exist, 
being in network or meshes as seems best for their pur- 
poses. So completely is the system penetrated by these 
little vessels that the slightest scratch or cut may produce 
bleeding from the surface. 

It would seem as if some of these vessels were at a great 
distance from the heart to be affected by its action, but the 
motion of the blood in the capillaries is doubtless due 
partly to that influence as well as to the natural elasticity 
of the vessels. The presence of capillaries in various parts 
of the body is readily shown by accidental causes, such as 
a grain of sand inducing a bloodshot eye. Blushing is an 
illustration also of the existence of capillaries, which under 
emotion become filled with blood. 

Velocity of the Circulation. — The velocity of the circu- 
lation is affected by friction, by gravity, by curves in the 



CIRCULATION. 163 

course of the vessels, by division into branches, etc. If 
gravity interferes with the rapidity of circulation in one 
direction, it must aid it in another, as in parts of the body 
in which the blood flows quickly downward in the arteries 
and more slowly upward in the veins. The physician bears 
this in mind in the posture in which he places his patient, 
his head being elevated if there be any inflammatory con- 
dition of that part, the leg elevated in affections of the foot, 
etc. By a wise provision, the main artery of supply of 
blood to the brain takes a curved and tortuous course 
rather than a straight direction to that organ, so that the 
force of the current may be broken before it reaches its 
delicate structure. 

Experiments have been made on animals to determine 
the rapidity with which substances introduced into the 
blood will return to the same point after having traversed 
the whole course of the circulation. These have proved 
that in most animals the rapidity of the circulation is equal 
to the time in which the heart makes twenty-seven pulsa- 
tions. If this be true of man, and his pulsations be 
seventy-two per minute, the blood would occupy about -f-J 
of a minute in passing successively through the heart, the 
capillary vessels of the lungs, the arteries, the general 
capillary system, and the veins, or twenty-two and a half 
seconds. This is surprisingly rapid, considering the deli- 
cate structures that the blood must necessarily permeate, 
and the amount of nutriment and other material it is con- 
stantly giving off in its course. 

Infusion and Transfusion. — By infusion is meant the 
introduction into the blood of various materials, such as 
medicines ; by transfusion, the introduction of fresh blood 
from one animal into the vessels of another. Both opera- 
tions were first performed in the seventeenth century. As 



164 PHYSIOLOGY. 

it was supposed that the cause of all diseases resided in the 
blood, it was imagined that all that was necessary was to 
replace the diseased fluid with pure, healthy blood. This 
process, which we call transfusion, is resorted to in cases of 
hemorrhage particularly, and in very low conditions of the 
system, when some extreme measure of this kind seemed 
absolutely necessary, has sometimes restored the patient to 
life. 

When medicines are introduced by infusion into the 
bloodvessels they act more rapidly than when taken by the 
mouth, and produce just the same effects. An emetic, for 
instance, will vomit rapidly in this way. When transfu- 
sion was first used, soon after the discovery of the circula- 
tion by Harvey, it was thought that the operation would 
give young blood to old persons, and restore the vigor and 
vitality of their earlier manhood, and it soon became a 
popular remedy. It is at the present day resorted to only 
in cases of utter prostration, as already mentioned, for the 
restoration of life. 

Circulation in Other Animals. — The circulation in the 
higher classes of animals — the mammalia, as they are 
called — is like that of man. The heart is composed of two 
distinct parts, each of which has its auricle and ventricle. 
In each case there is a double circulation, the greater and 
lesser, as already described. The situation of the heart 
differs, however, in some of them ; and in the pig and the 
stag there are two small flat bones, called bones of the 
heart, which are found where the aorta leaves the left ven- 
tricle. Other differences also occur, as with the otter, dol- 
phin, etc., some of the vessels of which are very large and 
tortuous, probably to act as a receptacle for the returning 
blood, while respiration is temporarily suspended during 
the existence of the animal under water. 



CIRCULATION. 



165 



In 6fVefe, the course of the circulation is very much the 
same as in man. The blood reaches the heart and is dis- 
tributed from it by arteries, veins, auricles, and ventricles. 
In the right ventricle, however, the valve is sometimes re- 
placed by a strong triangular muscle, which helps to force 
the blood from the right ventricle to the lungs. The lungs 
of a bird do not expand like those of man or the upper 
classes of animals, and therefore need this assistance. 

In the circulation of rep- 
tiles — as the tortoise and 
lizard (Figs. 64, 65)— there 
is but one ventricle, in- 
stead of two, and there is 
a direct communication 
between the arterial and 
venous blood. Only a 
portion of the latter be- 
comes purified in the lungs 
and mixes in the ventricle 
with the venous blood. 
There are usually two au- 
ricles — the left receiving 
the pure blood, the right 
the venous blood — both 
auricles discharging their 
contents into the common ventricle. It will be seen that 
the blood is but imperfectly arterialized, and it will be 
readily understood how, life being maintained with such 
imperfect aeration of the blood, the circulation may con- 
tinue when the animal is so placed as to be incapable of 
respiration. 

The circulation in fishes is very simple. The heart has 
but one auricle and one ventricle. The blood is propelled 




Fig. 64. — Circulation of the Tortoise. 

a, a, vense cavge ; b, right auricle; c, g, right 
and left ventricles united in one; d,d, pul- 
monary arteries; e, e, pulmonary veins; 
/, left auricle; », aorta; i, large artery— 
really a second aorta— uniting at k with the 
original aorta. 



166 



PHYSIOLOGY. 



Pulmonary circulation. 



Aorta. 



from the ventricle to the gills, where it is arterialized, as has 
already been stated under Respiration (p. 143). Having thus 
acquired its purified state by contact with oxygen, it passes 
into a large artery analogous to the aorta, and thence into 
the general circulation, but does not return to the heart 
until it has passed through the capillaries. It enters the 

auricle and theif goes to the 
ventricle, and thus the circu- 
lation is complete. The heart 
is extremely small in propor- 
tion to the body (Fig. 66). 

The circulation in insects is 
much more imperfect. They 
have neither arteries nor 
veins. The fluid which nour- 
ishes them seems to diffuse 
itself through their tissues. 
There is no heart, but a mem- 
branous tube runs along the 
back, in which alternate dila- 
tations and contractions are 
perceptible, and this has been 
considered by some to rep- 
resent a heart. The blood is 
watery and without color. In some of them there is a kind 
of movable valve, which gives a rapid movement to the 
circulating fluid. Insects differ, however, so much in their 
anatomy that no one description will apply to a sketch of 
the circulation in all. Some of the more highly organized 
seem to have bloodvessels, and in worms there is something 
very like a heart. The leech has no heart, but circulating 
vessels which dilate and contract. 

In other classes of animals, such as spiders, lobsters, 




Ventricle. 



Systemic circulation. 
Fig. 65. — Theory of Circulation 
in Reptiles. 



CIRCULATION. 



167 



Pulmonary circulation. 



Auricle. 



Heart. 



Veins 



crabs, snails, etc. (Fig. 67), there are other peculiarities of 
structure for purposes of a circulation. Some of the spiders 
have a more perfect circulation than insects. The blood is 
white, but in the more highly organized there is an elong- 
ated heart at the back, which sends out blood and receives 
it again through the lungs. In the lobster and other shell- 
fish there is a heart with 
one ventricle — but no 
auricle — and bloodves- 
sels, and also something 
like lungs. The veins 
constitute a sort of res- 
ervoir rather than reg- 
ular vessels. In snails, 
oysters, and animals of 
that class, the heart is 
composed of a single 
ventricle, from which 
the arteries pass, while 
the auricles are either 
double or single, and 
receive the red blood 
from vessels that seem 
to resemble the pulmo- 
nary veins, which in man carry the purified blood from 
the lungs. In the very lowest forms of animal life the 
blood or fluid which nourishes it is diffused by a sort of 
permeation or infiltration through the wall of the digestive 
tube, in the absence of either heart or vessels. 

The Blood. — Having now described the apparatus by 
which the blood is distributed to the various organs for 
purposes of nutrition, we naturally turn to consider the 
general properties of this fluid which adapt it for the per- 




Fig. 06. 



Systemic circulation. 
-Theory of Circulation in 
Fishes. 



168 



PHYSIOLOGY. 



Pulmonary circulation. 



formance of its duties. It is estimated that the entire 
amount of blood contained in the body of a grown person 
is about one-fourteenth of his whole weight. To enable 
it to maintain the nourishment of the body, the materials 
which enter into its composition should be the same as 
those which make up the body itself. This we find to 

be the case. In some of its 
properties it resembles the 
chyle, which we have al- 
ready seen was formed as a 
result of the digestive pro- 
cess, and which is absorbed 
into the chyliferous vessels 
in the intestines to become 
blood. It of course differs 
in color, but chyle and 
lymph are both rudimental 
blood. At first, when drawn 
from the arm, as in bleeding 
a patient — a practice that 
was formerly quite popu- 
lar — the blood does not 
seem to be the mixed fluid 
that it really is. It is of a 
dark color as it flows from the veins, and a bright red 
or scarlet in the arteries. It is about 100° in tempera- 
ture in man, but in some other animals much higher, as in 
the sheep, in which the temperature is 107°. It is heavier 
than water. 

The Blood-Globules. — If it were not for the microscope 
we should not know what parts blood is composed of. 
When submitted to examination by that instrument it is 
found to consist of a large number of minute red par- 




Systemic circulation. 
Fig. 67. — Theory or Circulation in 
Crabs, Lobsters, etc. 



CIRCULATION. 



169 



tides — microscopic bodies called blood-corpuscles, blood- 
globules, or discs — suspended 
in a thin fluid called the serum. 
These bodies are so minute that 
the smallest drop of blood on 
the point of a needle contains 
myriads of them. They are 
of a regular and definite shape 
in the same animal, but are of 
different form in different ani- 
mals. In the class of animals 
called mammalia, which in- 
cludes man and the animals 
next in the scale, the cor- 
puscles are circular, while in birds and cold-blooded ani- 
mals they are elliptical (Fig. 69). The human blood-cor- 




Fig. 68. — Human Blood-cor- 
puscles (magnified). 




7% • 




Fig. 69. — Blood-corpuscles op Various Animals (greatly magnified). 

a, a', blood-globules of man, seen under diff -rent views; b, of the camel; e, d, of 
birds; e, of the frog, seen edgewise;/, of the proteus; .9, of the salamander, 
the external membrane being stripped: h, of the lamprey; i, of the lobster; 
k, of the slug-snail; I, two white globules of human blood. 



puscles are flat discs, somewhat concave in the middle, with 
slightly rounded edges (Fig. 68). 

Some idea of their minuteness may be obtained from the 

15 



170 PHYSIOLOGY. 

statement that in man their average diameter is only the 
32 1 00 th of an inch, and their thickness the 12 oo "o tn of an 
inch. The serum in which they float is transparent and 
colorless, the redness being entirely due to the red cor- 
puscles. They do not appear to be so red under the micro- 
scope as in reality, but this is an optical effect produced by 
the thinness of the medium in which they are observed by 
the eye. Sometimes the corpuscles arrange themselves in 
rolls — or rouleaux as they are called, like coin piled up 
together — and then they seem of a redder color to the eye. 
The size of the corpuscles varies in different animals. We 
can readily understand how important it is to be able to 
distinguish under the microscope the difference between the 
corpuscles of man and other animals. In a case of sup- 
posed murder the life of one suspected of the crime might 
depend on the result of such an examination. It is not 
many years since the blood of a pig on the clothing of a 
supposed murderer placed the life of the prisoner in immi- 
nent peril. 

To show more clearly the varying size of the corpuscles 
in animals as compared with man, the following brief 
statement may be made, the measurement being first given 
of animals with circular corpuscles or discs, and afterward 
of those with elliptical corpuscles. 

Of animals with circular discs, a few examples will 
suffice : 

Diameter. 
Man ¥ 2V o inch. 



Elephant ^y 1 ^ 

e 3V <y 



Musk-deer 



In other animals which have elliptical blood-corpuscles 
the measurement must be taken both in length and 
width : 



CIRCULATION. 

Long Diameter. 

Camel 3^0 

Ostrich TT5 Vo 

Pigeon 2is\j 

Humming-bird 2eV^ 

Frog TT Vs 

Crocodile T ^\ T 

Shark jfa 

Earth-worm T ^ 



171 



Short Diameter. 



1 68T 
TIOO 



White Corpuscles. — White corpuscles are also found in 
the blood, of a spherical shape, and not so well denned as 
the red corpuscles, although somewhat larger in size. They 
are much fewer in number than the red, and have a more 
sluggish movement in the vessels. In healthy blood there 
is about one white or colorless corpuscle to every four hun- 
dred or .five hundred red corpuscles. These are consid- 
ered to be the globules absorbed into the blood from the 
lymphatic vessels and the chyle, and to become developed 
afterward into the red corpuscles. 

Number and Uses of the Red Corpuscles. — The number 
varies greatly in differ- 
ent animals, seeming to 
bear a pretty close ratio 
to the temperature. In 
all of them they are to 
be counted by millions. 
One estimate, generally 
considered accurate, is 
that five millions of 

them are contained in Fig. 70.— Blood-crystals. 

the space occupied by a very small drop of blood. Another 
authority has stated that if the colored corpuscles of the 
adult man were placed side by side on a flat surface they 
would cover an area of about 3000 square yards. The 




172 



PHYSIOLOGY 



higher the temperature the greater the number of the 
corpuscles. By chemical action beautiful crystals can be 
obtained from the coloring-matter of the blood, which 
under the microscope present the appearance presented 
in Fig. 70. The blood-globules are really carriers of 
oxygen, which they obtain in the lungs 
during respiration, as has been already 
shown, and bear with them to the differ- 
ent tissues. Parts which are in active 
exercise, such as the muscles and nerves, 
need this fresh supply of oxygen, and 
in the course of the wear and tear to 
which they are subjected give to the 
blood, by lymphatic absorption, a cer- 
tain amount of carbonic acid, which 
passes along with the blood, to be got- 
ten rid of in the lungs by expiration. It 
will be readily seen why hemorrhages 
are fatal or serious in character. Life 
can only be maintained as long as the 
blood-corpuscles are well organized and 
contain the proper proportion of oxygen. 
Fig. 71.— Coagulation An animal cannot survive the loss of 
of the Blood. ar , v i ar g e quantity of its blood. A cer- 

1, clot; 2, serum. ^ amount of j^ exigtg in the b ] Qod 

but not in any great proportion, probably not more than 
thirty grains in the whole body. 

Coagulation of the Blood. — Blood that is circulating in 
the body consists of two portions, the red corpuscles and a 
watery portion called the liquor sanguinis (" water or solu- 
tion of blood "). When blood is drawn from the body 
a rapid change takes place in it. Instead of a homo- 
geneous fluid, such as it is in the vessels, it becomes sep- 




CIRCULATION. 173 

grated in a short time into distinct portions — a reddish 
jelly-like, trembling mass, to which the name clot is applied, 
and a yellowish liquid called the strum. The cause of this 
change is due to the separation from the blood of an ele- 
ment in it called fibrin, which is soluble in living blood 
— if we may so call it — and insoluble in dead blood, or 
that which has been drawn from the bloodvessel. The 
fibrin leaves the liquor sanguinis, of which it formed a 
part, and draws down with it to the bottom of the cup or 
receptacle in which it has been received the red corpuscles. 
The clot is therefore the union of the red globules and 
the fibrin of the blood ; the serum is the thin liquid por- 
tion left behind, in which are dissolved the other ingre- 
dients of the blood (Fig. 71). 

The difference between circulating and coagulated blood 
may be clearly exhibited in the following diagram : 

Circulating Blood. Coagulated Blood. 

T - • • fkSerum. Serum. 

Liquor sanguinis J 

Fibril 



Corpuscles Clot. 

(The lines indicate the combination of the fibrin with the 
corpuscles to form the clot, while the serum is left alone.) 

Various attempts have been made to explain the causes 
of coagulation of the blood when exposed to the air, but 
this is one of those difficult points which do not admit of 
ready explanation. Some physiologists content themselves 
with calling it a " vital" process, which is a quiet admis- 
sion that they know nothing of its causes beyond the fact 
that it is in some way connected with the life of the blood or 
of the individual, and is not merely a physical process. All 
we know is, that there is in the blood an element called fibrin 
which becomes entangled with the corpuscles to form the clot. 

15* 



174 PHYSIOLOGY. 

Whatever its exciting cause, coagulation is an important 
means of stopping bleeding after a bloodvessel is cut by ac- 
cident or otherwise, the clots formed stopping up the open 
mouth of the vessel. In some animals, as birds, coagulation, 
or the formation of a clot, takes place instantaneously. Thus 
Nature seems constantly to guard the lives of some of the 
most helpless of her creatures by placing within their frames 
the elements of preservation of life itself, even when danger 
most seriously threatens it. It may be asked why the blood 
does not coagulate in the vessels during life when exposed, 
as it always is, to friction and motion. It does sometimes, 
but rarely, form clots, which block up the smaller vessels, 
and possibly a cavity of the heart, and endanger life, but 
while circulating in living tissues and brought in contact 

to to to 

with them coagulation is of the rarest possible occurrence. 



QUESTIONS. 



Through what fluid are all parts of the body nourished? 
What is the process called by which the blood is sent through the 
body ? 

What relation has it to digestion, absorption, and respiration? 

To which side of the heart does the blood go after leaving the lungs? 

What is the great central organ of the circulation? 

Why is the process called a circulation? 

Of what tissue is the heart chiefly composed? 

What is the shape of the heart? What is its position in the chest? 

What is its weight? Its size? 

What is the lining membrane of the heart called? 

What does the word endocardium mean? 

How is the heart covered ? 

What does the word pericardium mean? 

How many cavities are there in the interior of the heart? 

How many of these propel the blood? 

Is the heart a single organ? 

Which side of the heart receives the venous blood? 



CIRCULATION. 175 

To what organs does the venous blood pass after leaving the right side 
of the heart? 

Where does the blood go after leaving the lungs? 

What are the cavities of the heart called? 

Trace the course of the blood from the right auricle to the left ven- 
tricle. 

Into what set of vessels does the blood pass after leaving the left 
ventricle? 

What a,re arteries and veins ? 

What is the venous heart? The pulmonary heart? The arterial 
heart? The aortic heart? The systemic heart? 

What is the lesser or pulmonic circulation? 

What is the greater or systemic circulation? 

What is the object of each circulation ? 
Which side of the heart has the most labor to perform ? 
What arrangement is there to prevent the blood from flowing back- 
ward in its course? 

What is the valve between the right auricle and 1 ight ventricle called ? 
Why? 

What is the valve between the left auricle and left ventricle called? 
Who first discovered the circulation of the blood? 
What are the semilunar valves? 

To what are the regular movements of the heart due? 
What is the systole ? The diastole ? 

What is the nature of the movement of the auricles and ventricles? 
Does the heart have any rest from labor ? 
Where is the beat of the heart felt? 
What is the apex of the heart ? 
How is the movement of the heart facilitated? 
What is the impulse of the heart ? 

Is the heart made up of voluntary or involuntary muscular fibres? Is 
it under control of the will ? 

What effect on the blood in it has the contraction of the heart? 

Is there any limit to the contractile power of the heart? 

What heart-sounds are heard when the ear is applied over the chest ? 

Which sound is the longest? 

What is the cause of the first sound? 

Is it due to the impulse of the heart against the chest? 

What is the cause of the second sound? 

Describe the course of the blood through the auricles and ventricles. 

What is meant by the beat of the heart ? 



176 PHYSIOLOGY. 

What is the pulse? 

How many times does the pulse beat in a minute? 

How may this number be increased? 

What effect has position or attitude on the pulse? 

Has the pulse any relation to the quantity of blood ? 

What varying effects have excitement, emotion, etc. on the pulse? 

At what period of life is the pulse most rapid? 

In which sex is the pulse more rapid? 

What effect has sex on the size of the heart ? 

How often does the heart beat in a minute ? In a day? In a year? 

How much blood is sent out from the ventricles at each pulsation ? 
How many ounces per minute? 

What proportion of the weight of the body is the blood? 

How does this compare with other animals? 

What action have the semilunar valves of the heart? 

What is the duty of the arteries ? 

What is the largest artery in the body ? 

Why were arteries so named ? 

What coats have the arteries? 

What is the condition of the arteries after death? 

What is the mode of division of the arteries? 

Why do we feel the pulse at the wrist? What do we learn from the 
pulse? 

How are the arteries protected in various parts of the body? 

What is a sphygmograph ? What is its importance? 

What are the veins? How does a vein differ from an artery? 

W T hat is the difference between the flow of blood from a vein and an 
artery when cut? 

Is there any pulse in a vein ? 

What are the venae cava?? 

Do arteries or veins possess valves? For what purpose? 

Are valves present in all the veins? 

What are the capillaries? 

Through what vessels is nutrition effected ? 

What organs are most richly supplied with capillaries? 

What keeps up the movement of the blood in the capillaries? 

What vessels are interested in blushing or in a bloodshot eye? 

What effect has gravity on the rapidity of the circulation ? 

How is the force of the current of blood to the brain checked? 

W T hat do we learn from experiment as to the velocity of the circulation ? 

In what length of time does the blood pass through the body? 



CIECULATION. 177 

What is meant by infusion ? By transfusion ? 

Under what circumstances are these operations resorted to? 

What is the nature of the circulation in the higher classes of animals? 

In what respects do the heart or vessels of the stag, dolphin, etc. differ 
from those of man? 

What is the peculiarity of the arrangement for circulation in birds? 

How many ventricles has the tortoise? 

Is there any direct communication in them between the venous and 
arterial blood? 

What effect has this upon the purity of the blood? 

How many auricles and ventricles have fishes? How, then, is the 
blood arterialized ? 

What becomes of the blood in fishes after it leaves the gills? 

What organs are absent in some insects? What is the color of their 
blood ? 

How do insects themselves differ in their circulation? 

What is the nature of the circulation in spiders? In shell-fish ? In 
snails? 

How does the blood circulate in the very lowest forms of animal life? 

What proportion does the amount of blood in the body bear to the 
whole weight? 

What fluid formed in digestion resembles the blood ? 

What is the color of the blood in the veins? In the arteries? 

What is the temperature of the blood in man? In other animals? 

How does its weight compare with that of water? 

Of what parts is the blood composed as seen under the microscope? 

What is the shape of the blood-globules in man and the higher ani- 
mals? In birds? 

What is the size of the human blood-corpuscles? 

What is the importance of distinguishing between the shapes of the 
globules of man and of other animals? 

What other corpuscles are found in the blood? 

State from the table some of the animals that have the largest blood- 
corpuscles. 

How do the shape and size of the white corpuscles compare with those 
of the red corpuscles ? 

How many red corpuscles are there to every white corpuscle? 

What are the uses of white corpuscles ? 

What is said as to the number of the red corpuscles in the body? 

What are the uses of the red globules of the blood? 

Where do they obtain oxygen ? 

M 



178 PHYSIOLOGY. 

Where does the carbonic acid in the blood come from ? How is it 
got rid of? 

How much iron is present in the blood ? 

What change takes place in the blood when drawn from the body ? 

What are the two portions called ? 

What element separates from the blood to help form a clot ? 

What is the clot composed of? 

What is the difference in composition of circulating blood and coagu- 
lated blood ? 

What effect has coagulation on bleeding ? 

Does the blood ever coagulate during life ? 



ANIMAL HEAT. 



Temperature of Animals. — The temperature of the body 
characteristic of man and other animals is known as Animal 
Heat. It is in most animals a constant quantity ; that is, 
each animal has a temperature which does not usually vary. 
Such animals are known as warm-blooded, and the term 
cold-blooded has been assigned to those whose temperature 
is not constant and not much above that of the external 
air or the water in which they live. The temperature of 
the latter varies greatly also with conditions of the atmo- 
sphere, etc. surrounding them, and is considerably below 
that of the human body. Reptiles and fishes belong to 
the class of cold-blooded animals. The subject of Animal 
Heat is often taught in connection with that of Respira- 
tion, because the two processes are associated with or de- 
pendent upon somewhat similar chemical changes. 

Sources of Animal Heat. — In the process of respiration 
more oxygen is taken into the lungs than is given off again 
in the form of carbonic acid, of which oxygen is an ingre- 
dient. This excess of oxygen serves a useful purpose all 
through the body by uniting with the carbon and hydrogen 
which have been taken as food, and this union gives rise 
to the production of heat. When carbon thus combines 
with oxygen, their union forms carbonic acid ; and water 
is formed by the union of the oxygen and hydrogen. 
Every chemical change which occurs in the body results in 

179 



180 PHYSIOLOGY. 

the production of heat. We notice a similar result occur- 
ring during the germination and flowering of plants. 

Effect of Food, Respiration, etc. — The more active the 
process of respiration and the more generous the supply 
of food, the greater the amount of heat produced. Thus 
animals, such as birds, which have a particularly active 
process of respiration, evolve the greatest amount of animal 
heat, as shown by the general temperature of their bodies. 
Where the respiration is slow and inactive, as in reptiles, 
and the same amount of oxygen is not required, the tem- 
perature is not so high. Increased exercise, which gives 
rise to rapid breathing, elevates the temperature. In the 
Arctic regions a larger quantity of food, especially of an 
oily and fatty kind — which are composed of carbon and 
hydrogen — is taken than by the dwellers in milder climates. 
The influence of food upon the temperature of the body is 
shown also in the fact that the animal heat is reduced during 
starvation, and it is a well-recognized point that in such a 
condition freezing to death takes place very rapidly. 

Temperature of Different Organs. — The temperature of 
the body may be ascertained in various regions. When a 
thermometer is placed in the arm-pit, it registers in health 
from 98 ° to 100° (Fahrenheit), and the temperature of the 
body generally is stated to be 100°. When the bulb of 
the thermometer is placed in the interior of the mouth, as 
beneath the tongue, the same degree of temperature is 
recognized. Whatever it may be, it usually varies but a 
degree or two. In young children the temperature is about 
two degrees higher than in the adult. Of late years much 
attention has been paid by the physician to the study of 
changes of temperature in disease. Any decided variation 
above or below the standard is a subject for anxiety. In 
some affections, such as typhoid fever, there is an elevation 



ANIMAL HEAT. 181 

of temperature, while in cholera it may fall many degrees. 
In health any marked deviation is cheeked by the power 
of evaporation possessed by the skin and seen in the visible 
perspiration on the surface of the body. 

The temperature of the various organs, as the lungs and 
the muscles, is rather higher than that of the surface of the 
body. The blood is hotter on the right side of the heart 
than on the left, and cooler after it leaves the heart, the 
temperature having doubtless been lowered in the Lungs 
during the passage of the blood through them. The tem- 
perature is lower in the veins near the surface of the body 
than in the arteries, but in interior tissues and organs the 
blood coming from them by the veins is warmer than that 
going to them by the arteries. It has been thought by 
some that the heat of the body was produced by chemical 
action in the lungs during respiration, but this is not now 
considered to be the correct theory. If all the heat origi- 
nated there, the delicate structure of the lungs would be 
undergoing a process of incessant combustion, which would 
soon destroy it. 

Mechanical forces, such as friction, muscular movement, 
etc., also give rise to heat in varying quantities. The 
greatest amount of heat is produced in the liver and by 
the muscles, and it is found that the blood is warmer after 
coming from a muscle than it was in going to it. 

Atmospheric Influences, Clothing, etc. — Man, having a 
temperature nearly constant under all circumstances in 
health, and being able to regulate the proper quantity of 
his food and exercise, as well as to defend himself against 
intense heat or cold by regulation of his clothing, can tol- 
erate excessive heat or cold with much greater impunity 
than is possible with any other animal, whether warm- 
blooded or cold-blooded. Xo matter what the climate or 

16 



182 PHYSIOLOGY. 

season, the temperature of the human body remains very 
nearly the same. The thicker clothing with which man 
protects himself in winter prevents the loss of the heat of 
the body by radiation. 

The occupations of individuals sometimes render it neces- 
sary for them to be subjected to very high temperatures, 
such as those of iron-works, etc., but even under such cir- 
cumstances the temperature of the human body is not much 
affected. As already stated, there is a compensation for all 
this in the evaporation attending the increased amount of 
perspiration produced by such exposure. It is a well- 
known fact that during evaporation heat is abstracted, and 
the part becomes really cooler. The more rapid the evapo- 
ration the more decided the sensation of cold. In warming 
the rooms we occupy in winter we endeavor to prevent the 
heat of the body from being too rapidly lowered. The 
temperature of the body is always higher than that of any 
artificial heat we obtain or could bear in our residences. In 
cold seasons there is but a small amount of perspiration 
poured out, so that evaporation can produce but little cold- 
ness of the surface, and effect, if any, only a slight reduc- 
tion of temperature of the body. We shall hereafter, as 
part of the study of the physiology of the touch, investi- 
gate the action of the skin while engaged in this important 
duty of exuding the perspiratory fluid. 

We have thus traced the history and course of the blood 
from the time it was formed from food and lymph by Di- 
gestion and Absorption through its changes to a purer state 
in Respiration, and in its distribution through the body by 
the Circulation. The chemical changes involved in the 
production of Animal Heat take place through the agency 
of the capillary bloodvessels, which in myriads permeate 
even the minutest portions of the body. 



ANIMAL HEAT. 183 



QUESTIONS. 

What is meant by Animal Heat? 

Does the temperature vary much in the same animal? 

What are warm-blooded animals? 

What are cold-blooded animals? 

Give examples of the latter. 

Is more or less oxygen taken into the lungs than is given off from 
them? 

What purpose does this excess of oxygen serve in* the system? 

What is formed when carbon and oxygen thus unite? When hydrogen 
and oxygen unite ? 

By what kind of action is the heat of the body produced ? 

Does this occur in the vegetable ? 

What effect have food and respiration in the production of heat? 

How is this exemplified in birds ? 

When respiration is sluggish, how is the animal heat affected? 

What effect has exercise ? 

In the Arctic regions what is the relation of food to animal heat? 

What effect has starvation ? 

What is the usual temperature of the human body? Of the region 
under the tongue? 

How does the temperature of young children vary? 

What information does the physician get from the temperature? 

What effect has the skin in checking elevation of animal temperature ? 

Is the external or internal temperature the higher? 

On what side of the heart is the blood the hotter? 

Where is the blood of the heart cooled ? 

Is the temperature lower in the veins or the arteries? 

In what organ was all the animal heat at one time supposed to be 
formed ? 

W T hat mechanical forces produce animal heat? 

In what organs is the greatest amount of heat produced? 

Why is man able to tolerate excessive heat or cold ? 

What is the effect on animal heat of his thicker winter clothing? 

What effect has evaporation on the heat of the body ? 

How is the amount of perspiration and evaporation affected in cold 
weather ? 

What bloodvessels are concerned in the production of animal heat? 



SECRETION. 



Materials Separated from the Blood. — While the blood is 
going the round of the circulation, supplying nourishment 
at every point, the cells to which we referred in the intro- 
ductory chapter (p. 20) are busy taking from the blood 
various matters, which, being of no use in the system, must 
be partially or entirely separated from it. If it were not 
for some such arrangement as this, these useless materials 
would accumulate everywhere to the injury of the health, 
and would clog up the vessels so that the individual would 
surely die. This is the reason that such channels as the tears 
and the perspiration exist for getting rid of matters that are 
not nutritious. AVe have already stated that the cells every- 
where are endowed with the power of selecting from the 
b'.ood a special kind of material, just as if they had a mind 
of their own to guide them. Those cells, for example, 
which take materials from the blood with which to form 
tears always choose the same kind of materials, and never 
form anything else except tears, and tho.?e which form the 
fluid of the perspiration never create anything else than 
perspiration. 

Secretion only Separation. — In referring to digestion in 
the intestine, mention was made of the pancreatic juice and 
the bile, and the salivary glands were also alluded to in 
connection with the part performed by the mouth in diges- 
tion. These are all specimens of secretions, so called ; that 
is, of fluids separated from the blood by the action of 

184 



SECRETION. 185 

cells, for secretion means nothing more than separation. 
If there is any great amount of fluid separated in this way, 
there is a large organ or apparatus for the purpose. The 
bile, for instance, is secreted by the liver, which is one of 
the most important organs in the body. The simplest 
forms of separation of matters from the blood occur by a 
process like filtering from the delicate bloodvessels through 
a membrane ; and this is aided by the pressure of the blood 
itself. 

Glands. — The organ or body whose duty it is to separate 
materials from the blood is generally called a gland. Thus 
we have glands of the skin, which take matters from the 
blood to form the perspiration. The liver, pancreas, etc. 
are also examples of glands. They always have a canal or 
duct leading from them to carry off the fluid which they 
have been forming, and to empty it somewhere. The bile, 
for instance, is poured out by a canal (p. 104) into the in- 
testine ; the perspiration is poured over the surface of the 
skin through thousands and thousands of little tubes or 
canals leading from the sweat-glands. Sometimes, as in 
this case, there are many of these little tubes ; the gland 
over the eye, which forms the tears, being also another 
example of the same tubular plan. 

Various Kinds of Secreting Surfaces. — The simplest ar- 
rangement for purposes of secretion is an animal membrane 
and a minute bloodvessel (Fig. 72, 6, c). In other cases, 
as in that of more complicated organs, like the liver, the 
action of cells is necessary in addition to the membrane 
and vessel, because the power of selection is required. As 
the skin or any other form of membrane would not of 
itself give surface enough for the immense amount of work 
it has to do in separating materials from the blood, it is 
absolutely essential that the extent of surface should be in- 

16* 



186 



PHYSIOLOGY. 



creased in some way. This is done by one or more of the 
arrangements shown in Fig. 72, in which, by a turning in, 
or involution, as it is sometimes called, of the secreting 
membrane, room is given for a very large distribution of 
vessels, cells, and membrane, all of which are necessary 
to perfect secretion. A single inch of skin in this way 
becomes prolonged into a surface of many yards. This is 




Arrangement of Secreting Structures. 



A, a, cells; 6, membrane; c, capillary bloodvessels ; TC, simple glands, showing their 
different kinds of secreting apparatus; d, straight tube; e, sac ; /, coil of tubes; 
C, compound tubular gland; D, gland arranged like bunch of grapes; E, other 
shapes of glands. The dotted lines represent the layer of cells through the 
agency of which secretion is effected. 

not at all visible to the naked eye, and can only be seen 
under the microscope. Many thousands of such involu- 
tions of the surface and of such arrangements for secretion 
would thus occupy but a small amount of space. It will 
be noticed that some of the glands are tubular — that is, 
they are made up of tubes ; others are in shape like a 
bunch of grapes (Fig. 23), while others again are mere 
sacs. 

We need not dwell here upon the nature of the different 
secretions themselves. The tears will be referred to in de- 
scribing the physiology of the eye ; the perspiration in 
connection with the physiology of the skin as part of the 
organ of touch ; etc. 



SECRETION. 187 



QUESTIONS. 

What kinds of materials are separated from the blood? 

Why is it necessary that these matters shall be separated? 

What power have cells in selecting materials from the blood ? 

What kind of secretions are poured into the intestine during diges- 
tion? Into the mouth? 

What is meant by a secretion ? 

How is the simplest form of secretion effected? 

What is a gland ? 

W T hat are the principal glands found in the skin? 

How is the secretion of a gland poured out or emptied ? 

How are the bile and the perspiration poured out? 

What two parts are necessary in the simplest arrangement for secretion ? 

What other action is necessary in the larger glands ? 

What, then, are the three parts usually necessary to effect perfect 
secretion ? 

How is the extent of surface for secretion increased ? 

What are some of the shapes of the glands when seen under the 



THE NERVOUS SYSTEM 



A Function of Animals Alone. — A Nervous System is pe- 
culiar to animal life, having no existence in the vegetable. 
In this lies the one great feature distinguishing vegetables 
from animals. We have already seen that digestion, ab- 
sorption, respiration, and circulation take place in both ani- 
mals and vegetables. By means of a nervous system the 
animal is placed in direct communication with the world 
around it, and by it the different organs are able to act 
harmoniously together. It is developed in proportion to 
the scale of intelligence, and man therefore possesses a 
nervous organization which gives him a superior position 
over the whole animal kingdom.. By it man thinks and 
has sensation and voluntary motion. Even when uncon- 
scious, both men and animals are still controlled in their 
actions by a branch of the nervous system which is entirely 
beyond their power to control. Man lives although he may 
be asleep, and the nutrition of his body goes on whether 
waking or sleeping. It is very evident, therefore, that 
there must be a different nervous arrangement in charge 
of all such processes, and that there must be one portion 
entirely under his will, while another acts continuously and 
wholly beyond his control. In man, and all other animals 
which have a distinct nervous apparatus, we find it to be 
actually the case that there are divisions of the nervous 
system constituted in this way. 

188 




Fig. 73. — Cerebro-Spinal System. 
a, cerebrum ; b, cerebellum ; c, spinal cord ; d, nerve of face ; e, f, g, h, nerves of 
arm ; i, nerves between ribs ; k, nerves of lower part of back ; I, nerves in region 
of hip; m, n, o,p, nerves of leg. 

189 ■ 



190 PHYSIOLOGY. 

Divisions of the Nervous System. — One of these great 
nervous systems is regulated by the brain and spinal cord 
as centres, and is therefore called the cere'bro-spi'nal system 
(from cere'brum, " brain "), (Figs. 73, 75). Impressions are 
conveyed to and from these centres by slender white cords, 
called nerves, which divide and subdivide to extreme mi- 
nuteness until every part of the body is supplied with 
them. No matter how minute a section or an organ of 
the body may be, little branches of nerves are found in it. 
There is not a point of the surface, for example, which does 
not, when cut or pricked with a pin, show by the pain and 
suffering experienced that it is fully supplied with nerves. 

Another part of the nervous system is sometimes called 
the sympathetic system, because it brings all portions of the 
body into direct sympathy with one another, or the gan- 
glion' ic system, because, instead of having a brain or a spinal 
cord to control it, it has numerous enlargements called gang- 
lions or nervous masses, connected together by nerves so as 
to form one continuous chain (Fig. 84). This is a dis- 
tinct nervous system, but its nerves have communication 
with the nerves of the other system in order to make the 
chain of sympathy between the various organs complete. 
We can readily understand the importance of this action 
of sympathy when we reflect that all the duties which the 
organs perform must go on, either continuously or as often 
as required by the needs of the system. For instance, the 
gastric juice is only excited under the influence of the pres- 
ence of food, as already described under Digestion. This 
is an impression on the nerves of the stomach in the first 
place, through which the glands of that organ are stimu- 
lated to act. If it were not for a sympathetic nervous sys- 
tem, through which all the organs can communicate and 
sympathize with one another, each organ would be acting 



THE NERVOUS SYSTEM. 



191 



in its own independent course, and health and harmony 
would be impossible. We shall describe this great sym- 
pathetic system of nerves more fully hereafter (Fig. 84). 
Nervous Matter. — This is a soft substance, almost fluid at 
birth and for a short time afterward. When viewed under 
a microscope it is found to be made up of a white and a 
gray matter. The nervous matter generally is composed 
of the white substance, which is arranged in delicate nerve- 
fibres about the 6 q 00 of an inch in diameter. The gray 
or ashy-colored nervous matter is composed of nerve-cells 
of various sizes and in large quantity. They are comewhat 




Fig. 74.— Various Fokms of Nkrvr-Cklls. 

rounded, with a nucleus or central spot on each, with elon- 
gations running off in various directions (Fig. 74). A 
ganglion is usually a collection of these nervous elements 
massed together, the gray matter being in excess. Some 
of the physiologists, who think the nerves begin at the 
surface of the body, consider that the brain and spinal cord 
are ganglia in combination with the white matter derived 
from the nerves. White fibres are largely found in the 
long cords called nerves, which pass to and from the various 
parts. The exterior of the brain is made up of gray ner- 
vous matter ; the interior, white matter. The gray matter 
originates nervous power; the white conveys it. 



192 



PHYSIOLOGY. 



cord. 



Tho Cerebro- Spinal System. — The central parts of 

the cerebrospinal system 

(Figs. 73, 75) are the 

brain and the spinal cord, 

both of which are soft 

masses of white and pray 

fe J cere- 
matter, variously arrang- beiium. 

ed in these different or- Spinal 
gans. Taking the mass 
altogether as found in the 
spine and in the skull, it 
is called the cerebro-gpinal 
axis. The part contained in 
the skull is the brain ; that 
in the spine is the spinal 
cord, or spina/ marrow, as 
it is sometimes called. 

All these parts of the 
nervous system (Fig. 75) 
are protected from injury 
by bones and by mem- 
branes covering them. For 
instance, in the case of the 
brain, a blow or a fall on 
the head would affect that 
delicate organ much less, 
on account of the covering 
of bones and membranes 
with which it is protected, 
than if the brain had been 

nearer the surface, greatly Fig. 75. — Thk Bratn and Spinal Cord. 

exposed to external injury. The brain and spinal cord are 
both covered with three coats, one within the other, the 



Spinal 
cord. 




THE NERVOUS SYSTEM. 193 

outer coat being thick and strong, adhering in some places 
to the bones, and (lipping down between folds of the brain 
to form a kind of partition for its protection from pressure 
from the other hemisphere or from the cerebellum. 

One of these coats is like a spider's web, so thin and 
delicate is its structure. Between this membrane and the 
next one is a space filled with a liquid, called the cere'bro- 
spi'nal fluid. It seems to have been placed there to pre- 
vent the surfaces of the brain from rubbing against one 
another, just as oil is poured on parts of machinery that 
come into contact with other parts. If it were not for this 
fluid, the head when moved on the spinal column, when 
bent in Avalking or stooping, would press on the delicate 
nervous matter and injure it. In the middle coat are 
thousands of little bloodvessels running in all directions. 
The membrane not only itself protects these small vessels, 
but acts like a breakwater in diminishing the force of the 
current, which would otherwise injure the brain. 

The Brain (Figs. 73, 75, 76, 79). — This wonderful organ, 
placed in the skull, is really divisible into three distinct 
parts, all associated together. These are the brain, or cere f - 
brum, the large round mass which fills the upper, middle, 
and front portions of the skull ; the little brain, or cerebel- 
lum, a smaller, flattened portion at the lower and back 
part of the skull ; and a still smaller part, the medul'Ia 
oblonga'ta, which, translated into English, means the spinal 
cord prolonged (into the skull), for it is only the extension 
upward of that important portion of the nervous system. 
There is a large opening in the under and back part of the 
skull, which is placed there for the very purpose of admit- 
ting this organ to pass through it. There is a part of the 
brain which acts as a bridge between the cerebellum, or 
little brain, and the medulla oblongata, and this has been 

17 N 



194 



PHYSIOLOGY. 



called the pons Varo'lii, or bridge of Varolius, an anatomist 
of Italy, who first described it. 

If we should measure the amount of space in the skull 
occupied by the whole brain, Ave would find that seven- 
eighths of it belonged to the cerebrum, or brain proper. 
This part of the brain is the seat of the intellect or intelli- 

Convolutions. 




Cerebell 



Pons Varolii. 
Medulla oblongata. 



Fig. 76. — Interior of the Brain — showing, by section through it, its 

various parts. 

gence of the animal, and man has a greater amount of it, 
in proportion to the whole brain, than is possessed by any 
other animal. 

Weight and Size of the Brain. — The average weight of 
the brain of man is generally about 50 ounces, or a little 
over three pounds. The brain of the other sex is gene- 
rally from four to six ounces lighter. The usual weight is 
between 46 and 53 ounces in man, and between 41 and 
.47 ounces in woman. The weight of the brain goes on 
increasing rapidly up to the seventh year, and more slowly 



THE NERVOUS SYSTEM. 195 

up to the age of fort) 7 , when it reaches its maximum weight. 
With the advance of age and the decline of the mental 
faculties the weight diminishes. It has been found by 
examination after death that some persons with brains of 
light weight have exhibited strong intellectual power, and 
others who possess heavier brains have not displayed any 
great claims to intellectual brilliancy. The brain of an idiot 
seldom weighs more than 23 ounces. Some human brains 
have been found after death to weigh between 60 and 70 
ounces. The quality of the material that makes up a brain 
must be an element of as much importance as the weight. 
The brain proper of man is greater in proportion to the 
weight of the body than that of any other animal. One 
would think that the elephant or the whale would possess 
a much greater amount of brain than man, for their heads 
are so largely developed ; but it is found by examination 
that the brain of the elephant weighs only 120 to 150 or 
160 ounces, and of the whale about 80 ounces. This is a 
much smaller amount of brain, in comparison with the 
size of the animal, than that of man. The brain of the 
elephant is only the -5-J-oth part of the weight of the whole 
body, while in man it is about the ^th. The horse's brain 
is not half that of man's in weight, and yet his body is at 
least six times as heavy as that of man. 

The average proportion of the weight of the brain to 
that of the body in different classes of animals may be 
briefly stated, although there are individual exceptions to 
this statement: 

Fishes 1 to 4000 or 6000. 

Keptiles 1 to 1500. 

Birds 1 to 220. 

Man 1 to 40. 

Mammalia, including the higher animals 1 to 180. 



196 PHYSIOLOGY. 

The development of the brain is in proportion to the 
intelligence of the animal, so that in the lower scales of 
creation we find that organ occupying a very small part of 
the structure of the animal, and parts of the brain that are 
not concerned in intellectual uses largely developed. 

Brains of Different Races. — Several plans have been 
adopted to determine the actual amount of brain possessed 
by the different races of mankind. It has been found that 
the Caucasian race, examples of which are seen in the 
European and American, has the brain more fully devel- 
oped than any other. One mode of measuring the capacity 
of each race was to take the empty skulls of different races 
of men, weigh them, and, after filling the cavities with 
small shot, again weigh them, to find which contained the 
greatest amount of shot. This only showed, however, 
which would hold the most brain-matter in mass, but did 
not prove that one possessed more cerebrum or brain prop- 
er than the other ; and that was the only test of intellect. 
AVlien we look at the skulls of different races of people we 
find that the front part of the skull of the Caucasian race 
admits of a larger space for the brain proper, the seat of 
intellect. 

Facial Angle. — As the portion of the brain immediately 
in the front part of the skull is the seat of the highest 
intellectual development, the prominence of the forehead 
has been considered in man and animals a sign of intelli- 
gence. Its measurement has therefore been adopted as a 
test of the amount of actual brain-power. The facial 
angle, as it is called, which is formed between the forehead 
and the face, as shown in Figs. 77, 78, is the test employed. 
The angle formed by the meeting of the two lines ab and 
cd represents the prominence of the front part of the brain, 
and also the relative amount of intelligence. The great 



THE NERVOUS SYSTEM. 



197 



difference in this respect between the fully-developed Euro- 
pean and the imperfectly-formed head of the idiot is well 
exhibited. It will be noticed how defective the front and 
upper portion of the skull is in the latter, and how little 
room is left there for occupation by the brain. The angle 
in one case is almost a right angle ; in the other, quite 
acute. In monkeys the angle is much more acute. 

The Brain Proper. — The anatomists have given names 
to every little point or depression on the surface of the 









Fig. 77. 



Fig. 78. 



The Facial Angle. 
A, European ; E, idiot. 



brain, but with these we have very little to do, as we should 
be confused with a mere mass of names, without knowing 
the uses of any of the parts so called. As will be noticed 
in the illustration (Fig. 76), the cerebrum, or brain proper, 
is made up of numerous thick, worm-like folds or coils, 
called convolutions, and these are divided by several deep 
cracks or fissures — so deep that in looking at the brain in 
particular positions it seems as if it were cut in two (Fig. 
79, 2,2). It extends from the forehead in front to the neck 
behind, and from ear to ear. The chemist has analyzed 
the brain, but he finds it chiefly made up of fat and phos- 



198 



PHYSIOLOGY. 



phorus. The vital principle through which this fatty mass 
thinks and acts is beyond his power to fathom. The prin- 
cipal fissure of the brain divides it into two parts, called 
heinispheres (Fig. 79, 1, 1). 

The outer part of each hemisphere is made up of gray 
or ashy-colored matter, but the interior is almost entirely 

2 




Fig. 79. — Exterior View op the Brain. 
1, 1, right and left hemispheres of hrain ; 2,2, fissure, dividing brain into two parts. 

white nervous matter. Fibres passing upward from the 
spinal cord and medulla oblongata connect this with those 
parts, and fibres pass across also from one side of the cere- 
brum to the other. At the base of the brain are also other 
bodies, called ganglia, made up of gray matter, through 
which the fibres pass from below upward to the cerebrum. 
There is quite a variety of cavities or spaces, with arches and 
delicate veils and apparently mysterious halls and passage- 



THE NERVOUS SYSTEM. 199 

ways, which we suppose to be necessary for the perfection 
of the brain's duties, but we know little or nothing of the 
uses of each minute part or space, and merely study it as a 
whole, as the seat of all intellectual power and thought. 
Judgment and reason and memory have here their seat. 

The Lessons of Disease. — Much that is known about the 
work done by this portion of the brain has been learned 
from cases which have come into the hands of the surgeon 
in which the skull has been fractured or the brain injured. 
In such cases the powers of intellect and memory are de- 
stroyed, either for the time being or permanently. A defec- 
tive memory is one of the first indications of apoplexy or 
of some other disease or degeneration of the substance of 
the brain. In idiots it is one of the first symptoms that 
makes us suspect there is something wrong in the child's 
brain. Judgment and reason may be deficient for similar 
reasons, thus proving, from what we know of the effects 
of disease or injury, what are the functions of the organ 
when in perfect health. The physician is thus aided by 
pathology, or a diseased state of an organ, in discovering 
the nature of its physiology. 

Cerebellum. — The little brain, or cerebellum (Figs. 73, 
75, 76), is differently arranged from the cerebrum. It is 
not formed into convolutions or coils, but is, if we may so 
phrase it, in layers and foliated like the leaves of a book. 
On making a cut into it for examination a beautiful appear- 
ance is presented, called, from its peculiar tree-like arrange- 
ment, the ar'bor vi'tce, or "tree of life." This is due. to 
the extension of the white matter on its outer border into 
the gray matter of its interior, as shown in Fig. 76. 

Spinal Cord (Fig. 73). — As already stated, the medulla 
oblongata is an extension upward of the spinal cord. This 
cord, or spinal marrow, as it is sometimes called, is really a 



200 PHYSIOLOGY. 

combination of cords of nervous matter, separated by fissures 
or cracks running their whole length, and covered by a 
common sheath of membrane. Before passing upward 
into the skull the fibres from the right and left sides of 
the cord intersect one another, and then unite in the me- 
dulla oblongata, ascending into the pons Varolii, and thence 
into the cerebrum, in which they spread out in all direc- 
tions. It thus seems that the fibres of the right side of 
the body cross to the left side of the brain, and of the left- 
side to the right side of the brain. Each side of the brain 
therefore exercises some control over the movements of the 
opposite side of the body. We have yet much to learn of 
the physiology and minute structure of this and other parts 
of the nervous system. Paralysis may result from injury 
at these points in the brain, and, on account of the crossing 
of fibres to which we have referred, an injury of the 
right side of the brain may produce paralysis of the left 
arm or left leg, or vice verm. There is a similar crossing 
of some of the fibres of the spinal cord connected with the 
general sensation of parts, and loss of sensation on the op- 
posite side sometimes occurs. 

The Nerves (Figs. 80, 81). — These are continuous threads 
of nervous tissue which are distributed to all parts of the 
body. The nerves themselves are made up of collections 
of nervous filaments bundled together. Each filament is 
composed of a fine gray thread, surrounded by a soft white 
substance, enclosed in a thin covering or membrane. On 
the skin they are very largely distributed. They are gen- 
erally considered to arise from the brain or the other ner- 
vous centres, and convey impressions backward and for- 
ward, to and from the surface of the body or from organ 
to organ within the body. They are the telegraphic wires 
through which the will and the intellect and life itself 



THE NERVOUS SYSTEM. 



201 



make themselves manifest. They seem to be lost in the 
substance of organs, or, if they ter- 
minate on the surface, in minute 
nervous papilla? or points. They 
are either connected in this way 
with motion, as when distributed 
to the muscles, or with the nutri- 
tion of the body in the interior 
organs. After a nerve leaves the 
deeper structures, in which it is 
protected from injury, and comes 
to parts in which, by motion of the 
limbs or by pressure, it might suffer 
in any way, it becomes covered with 
a strong white fibrous sheath, which 



binds together the different fila- 




Fig. 80. 



A Nerve, Natural 
size. 



ments. This is called the nerve 
sheath, or neurilem'ma. 

In the course of some of the nerves are enlargements or 
knots called ganglions. These are especially met with in 
the great sympathetic nerve, already referred to, which in 







some mysterious way presides over 
functions, like secretion, digestion, 
circulation, etc., that are entirely 
beyond the control of the will. 
The communications between 
the nerves are not like those which 
take place between arteries and 
arteries and veins and veins, by 
open canals. There is no strict 
analogy between the bloodvessels 
and the nerves in this respect, for in the former the fluids 
actually mix, but when one or two nerves unite to form a 



a b c d e 

Fig. 81. — Nervic-fibres. 
a, b, e, d, nerve-tubes of different 
sizes; e, nerve-tube from syui- 
paf 



letic. 



202 PHYSIOLOGY. 

single cord there is no mixture of nervous matter, for they 
merely lie side by side without union. In Fig. 81 are 
shown the various appearances of the nerve-fibres from 
different parts. They are very distinct from the nerve- 
cells previously alluded to. 

The Nerves Symmetrical. — All the nerves of the cerebro- 
spinal axis come off from the base of the brain or from the 
spinal cord. The nerves come off in pairs — that is, one 
from each side of the axis, right and left, each correspond- 
ing to the other in shape, etc. For illustration : if the 
body be considered to be divided into two equal parts, 
right and left, by a section directly through the middle 
of it, it will be found that the two sides of the body are 
precisely alike and symmetrical. Every member, every 
organ, every vessel on one side, with few exceptions, will 
be found to have a fellow similarly placed on the other 
side, except, of course, such organs as are single, like the 
liver and heart, and occupy portions of both sides. The 
same is true of the nerves of the body, a similar sym- 
metry existing, the nerves issuing in pairs and from each 
side. 

It is usual among anatomists to name the nerves in the 
order in which they come off from the cerebro-spinal axis, 
beginning with the brain, but they do not continue calling 
them by number in regular series all the way down the spinal 
cord. Those which come directly from the brain and spinal 
cord number altogether forty-three pairs, but those which 
issue from the base of the brain are called cra'nial nerves, 
because they come from the cranium or skull, and those 
from the spinal region, spinal nerves. It is usual to say 
that there are twelve pairs of cranial nerves and thirty-one 
pairs of spinal nerves. The former, coining from the brain, 
pass out to various organs through openings in the skull or 



THE NERVOUS SYSTEM. 203 

bony covering of the brain, while the spinal nerves emerge 
through openings in the bony spinal column. Some phys- 
iologists take an opposite view, and consider that the nerves 
originate in the skin and muscles in different parts of the 
body, and pass inward to the spinal cord, instead of origi- 
nating in the nervous centres and passing outward to the 
skin, etc. Under this view they describe the spinal cord 
as made up of filaments derived from all the nerves of the 
external parts and the limbs. The brain itself they con- 
sider a round nervous mass or expansion formed by the 
upper part of the spinal cord projected into the skull. 

Cranial Nerves. — It is not necessary to go into a descrip- 
tion of these cranial nerves except in a general way. They 
supply the organs of sight and smell and hearing, the face 
(Fig. 82), the mouth and tongue and throat; and some of 
them are distributed to the heart and lungs and stomach. 
The first pair is called the olfactory nerve (from two Latin 
words which mean "causing to smell"), because it is the 
nerve of smell, sent to the nose to appreciate odors. The 
second nerve is the optic nerve, because it is the nerve of 
vision, which if injured destroys sight, no matter how per- 
fect the rest of the eye may be. 

The fifth pair of nerves is distributed to the face, the eye, 
the nose, the mouth, etc., and gives feeling and general sen- 
sibility to the parts it supplies, and adds also to the per- 
fection of the senses of taste, touch, etc. It is one of the 
most important pair of nerves in the body, and many of its 
branches are represented in Fig. 82. A recent writer in an 
English magazine states as a curious fact that people of all 
nations are accustomed, when in any difficulty, to stimulate 
one or another branch of the fifth nerve and quicken their 
mental processes. Thus, some persons when puzzled scratch 
their heads, others rub their foreheads, and others stroke or 



204 



PHYSIOLOGY. 



pull their beards, thus stimulating branches of the same 
nerves. Many when thinking have a habit of striking their 
fingers against their noses, and thus stimulating the branches 
distributed to the skin, while some people stimulate the 




Wilw 
Pf,§r <4 

.„„, \ / :;"A 



Fig. 82. — Superficial Nerves of tiie Face and Neck. 

(The guiding lines indicate the most important nerves and their branches. Their 

names are purposely omitted, as unimportant to the reader.) 

branches distributed to the mucous membrane of the nose 
by taking snuff. One man will eat figs while composing a 
leading article, others will smoke cigarettes, and others sip 



THE NERVOUS SYSTEM. 205 

brandy and water. By these means they stimulate the 
branches of the fifth nerve distributed to the tongue and 
mouth, and thus reflexly excite their brains. Neuralgia 
of the face is dependent on some irritation or disease of 
this fifth pair of nerves. An examination of the structure 
of these nerves gives no insight into the duties they have 
to perform. 

Some of the cranial nerves are connected with motion 
of the face, as in the expression of emotion, etc. ; some are 
merely nerves of special senses, like hearing and sight, and 
have no other function. These would give no indication 
of pain if cut or injured. When several nerves are dis- 
tributed to the same organ — the tongue, for example — the 
duty of one of them will be to supply the special sense, as 
taste, for example ; of another, to produce motion through 
the muscles of that organ j of a third, to give general sen- 
sibility to it, as evidenced by pain when it is scraped or 
injured in any way. 

Spinal Nerves. — These, as they issue from each side of 
the spinal cord, have two roots, which, approaching each 
other, join to form the nerve before its exit through the 
opening in the spinal column previously spoken of. It may 
be here stated that the substance of the spinal cord consists 
of gray and white matter, but differently arranged from 
that observed in the brain. Here the outer or cortical part 
of the nervous matter is the white substance, while the in- 
terior is the gray. The amount of white matter is greatly 
in excess of the gray. Three coats cover the cord, similar 
to those of the brain, and the cerebro-spinal fluid fills a 
similar space. The fibres which make up the larger or 
posterior root of each spinal nerve are nerves of sensa- 
tion, while those which form the anterior or lesser root 
are nerves of motion. On the posterior root is a small 

18 



206 



PHYSIOLOGY. 



ganglion or swelling (Fig. 83). There are two bundles or 

columns of white matter on the 
back of the spinal cord, with 
which the sensitive fibres of the 
posterior roots are connected, 
and two columns in front, with 
which the motor fibres of the 
anterior roots are connected. 
These are known as the pos- 
terior and anterior columns of 
the cord. 

Effect of Injury on Nerves. — 
When the spinal cord is injured 
or destroyed, or when the spinal 
column is broken, motion and 
sensation may, either one or 
both, be affected by the wound 
or by pressure of the broken 
bones. Every one is familiar 
with the sensation of a hand 
or a foot being " asleep." This 
is caused by temporary pressure 
on the nerves going to those 
parts from sitting or leaning 
upon them, numbness and want 




Fig. 83.- 



-Origins of the Spinal 
Nerves. 
The spinal cord is represented in the 
cut. A, A, A, anterior roots arising 
by minute divisions which unite 
afterward to form the fibres of the 
root; P, P, P, posterior roots; c, d, 
filaments passing between the po s : ° f power being the chief facts 
terior roots; g, g, g, ganglions of noticed. When a nerve is Cllt 
posterior roots; to, to, mixed nerves . -, 

formed by reunion of two roots. « r torn, motlOll and Sensation 
(The size of the roots is exaggerated.) are k otn \ QS ^ to the parts be- 

yond. The muscles cannot act, for the telegraphic wires 
are broken and they do not receive the message, and the 
skin feels dead to all sensation because the sensory nerves 
do not go beyond the gap thus made. Paralysis, or loss 



THE NERVOUS SYSTEM. 207 

of power of motion and of sensation, results, but if a por- 
tion of the nerves escapes injury the parts supplied by them 
will not be paralyzed. Motion and sensation are both lost 
at the same time, because both kinds of fibres lie side by 
side in the nerves affected. The kind and degree of the 
paralysis vary with the part of the spine involved. Thus, 
if the nerves in the middle of the back are injured, paralysis 
of the legs only will result. The arms would only become 
paralyzed if the upper jiarts of the spine, from which* the 
nerves supplying the arm are given off, are involved. Mo- 
tion and sensibility are generally lost together, but if the 
anterior column of the cord is alone affected, there will 
only be loss of motion, and of sensation in the case of the 
posterior column. 

When a nerve is cut across by accident or by the knife 
of the surgeon in operating, its power is not necessarily 
destroyed for ever. The nerves are so liberally supplied 
to all parts of the body that the slightest injury must 
affect some of them. Permanent loss of motion or of sen- 
sation very rarely results, because the nerves heal up by 
growing together again, not exactly as the skin or the flesh 
does, and not so rapidly. 

How the Spinal Cord Terminates. — The spinal cord does 
not descend in a continuous mass the whole length of the 
spinal column. At a certain distance down it ends in a 
bundle of nerves which pass off after the manner of a 
horse's tail, and is therefore called the caud'a equi'na — 
which is the Latin for a horse's tail — the nerves from 
which continue to pass out from the holes in the spine in 
the same way as the nerves in the upper part of the cord. 
The nerves which are distributed from the spinal marrow 
convey sensibility and power of motion to the most dis- 
tant points. Where they terminate they are sometimes so 



208 PHYSIOLOGY. 

minute as to defy the powers of the microscope. In their 
course they are a collection of nerve-fibres contained in a 
common sheath or neurilemma, as it is called. 

It seems impossible to find out, even with the micro- 
scope, whether each nervous thread goes on continuously 
from the brain through the spinal cord, or -whether these 
parts and the nerves are all connected with one another by 
other fibres. 

Nerves of Respiration. — Some^of the spinal nerves are 
distributed to the muscles of respiration, such as the inter- 
costal muscles — those between the ribs — and to the dia- 
phragm.. We have already seen how important this mus- 
cle is in the act of breathing — ordinary gentle breath- 
ing being effected by its rise and fall, without calling 
into full play the other muscles of the chest and abdomen. 
The intercostal muscles, by their action, raise and lower 
the ribs. We can readily imagine the result of an injury 
to the spine which would paralyze these muscles. If both 
nerves are cut, or the spinal cord is divided above them, 
death must result from stoppage of respiration, for the 
diaphragm will no longer rise and fall, being deprived of 
its nerve of motion, and the intercostal muscles will not 
aid the ribs to move. 

The Great Sympathetic Nerve (Fig. 84). — It has already 
been stated that a series of small bodies or ganglia of 
nervous substance, connected together by nervous cords and 
threads, and communicating with the other great nervous 
systems, is found spreading itself everywhere, through the 
chest and abdomen particularly. As will be seen in Fig. 
84, it is principally distributed in a symmetrical manner 
on each side of the middle line in front of the spinal col- 
umn. It has a seat also in the brain, from which muscles 
of the eye and ear and other organs of sense are supplied. 



THE NERVOUS SYSTEM. 



209 




Fig. 84. — The Great Sympathetic Nerve. 



1, 2, 3, ganglia in the neck ; 4, spinal ganglia; 5, branches in neck and chest going 
to heart ; 6, nerves to heart ; 7, nerves about diaphragm ; 8, nerve to digestive 
organs ; 9, semilunar ganglion ; 10, 11, 12, masses of nerves to abdomen ; 13, small 
nerves going with arteries to brain. Dotted lines indicate the position of a, the 
heart, and 6, the diaphragm. 

18* 



210 PHYSIOLOGY. 

It presides over involuntary functions associated with the 
maintenance of life, such as digestion, respiration, circula- 
tion, secretion, etc., but has nothing to do with the great 
mental or moral acts or with the motion of parts. These 
are influenced by the cerebro-spinal system. 

The small bodies, or ganglia, which are found in the 
course of the sympathetic nerves (Fig. 84) have been gene- 
rally considered by physiologists as centres of nerve-force — 
little brains, if we may so call them — which originate nerv- 
ous power and send it speeding along the nervous wires to 
the various organs. It seems a confirmation of its influ- 
ence in carrying on such important labors as are involved 
in digestion, respiration, etc. that the sympathetic system 
of nerves is developed before the other portions of the 
nervous system. It is a wise provision that places these 
important processes beyond the power of the will ; other- 
wise our lives would be made miserable with efforts of 
constant attention directed to the execution of these 
vital acts. Sympathetic branches are supplied to the 
muscular coats of the bloodvessels, which have the power 
of regulating the calibre or capacity of such vessels, and 
therefore the quantity of blood they may contain. A 
familiar example of this influence is seen in the act of 
blushing, or in the pallor which sometimes instantaneously 
covers the face. In some of the lower forms of animal 
life it has a separate and distinct existence in the entire 
absence of brain or spinal cord. 

Functions of the Nervous System. — The greatly diversi- 
fied arrangement of the brain and spinal cord shows that 
the nervous system is intended to fulfil a varied series of 
duties in carrying on life. Otherwise, what would be the 
necessity of this complicated structure, this division of two 
kinds of matter, gray and white, or the variety in form 



THE NERVOUS SYSTEM. 211 

and material of the different parts composing the nervous 
system? Physiology cannot here trace the exact relation 
of parts to the duties to be performed, as can be so readily 
done in machinery operated by physical causes. It has 
discovered much, but it is restricted in its inquiries. Living 
and dead animals have been experimented upon, with the 
view of increasing our knowledge, and diseases and inju- 
ries of the nervous system of man have also given us 
information as to the functions of the nervous system. 
The effort has often been made to find out the uses of 
every prominent point in the brain — for example, by stim- 
ulating it with electricity, etc. — but without much result. 
What has been learned from all these sources may be 
briefly stated. 

Functions of the Nerves. — When an impression is made 
on any part from without — as by a blow, or by tempera- 
ture, as heat or cold, etc. — it is received by the minute 
nervous threads which are present in every part, and con- 
veyed along them to the brain, which is the great central 
organ of sensation and perception. The impressions thus 
conveyed are the sensations with which we are so familiar. 
The brain is also the seat of volition, or of the will ; and 
the nerves, returning to the part affected, have the power 
of receiving another impression from the brain, and of 
transmitting it to a particular muscle or organ. They can 
thus call into motion, under the influence of the will, the 
muscles which it selects as the agents of its exercise, or 
stimulate other organs to action. It will thus be seen that 
there are two sets of nerves — already described — endowed 
with different functions, one set called sens'ory nerves, or 
nerves of sensation ; the other set communicating motion, 
and called motor nerves. The reason of this difference of 
function cannot be explained. They may run closely to- 



212 PHYSIOLOGY. 

gether in the same nervous sheath, but without any com- 
munication with one another. 

If the nerve connecting the limb of an animal with the 
nervous centres, as the brain or spinal cord, be exposed 
and mechanically irritated, two effects will follow : pain 
will be manifested, and the limb will be thrown into 
spasms. So, too, if the hand be accidentally brought into 
contact with a hot substance, a sensation of pain is commu- 
nicated to the brain by the nerves of sensation, and the 
hand is at once removed by an impulse sent through the 
nerves of motion. The fibres of motor nerves are dis- 
tributed through the substance of the muscles. When we 
hereafter describe the Skin we will understand more clearly 
the mode in which the nerves of sensation arise on the sur- 
face of the body before passing inward from the skin to 
the nervous centres. 

Reflex Actions of the Spinal Cord. — These are actions 
continually taking place in the body from impressions 
made from without, which are not under the control of 
the judgment or the will. They show that when the brain 
is not active, as during sleep, or after injuries which cut 
off communication between the brain and the external part, 
the spinal cord can take notice of the impression, and act 
in response to it. Sometimes voluntary motion may be 
destroyed in some way, and yet, if any irritation be applied 
to the skin of the part which has been paralyzed, the 
muscles will act temporarily independent of the will. It 
has been noticed in those Avho have entirely lost the use 
of their lower extremities that a spasmodic action of the 
muscles of the affected part may take place from the 
impression of cold or the striking of some other body 
against it. The brain does not control the action, for its 
communication has been cut off. The power to regulate it 



THE NERVOUS SYSTEM. 



213 




lies in the gray matter of the spinal cord, which is deeply 
seated and runs the whole length of the cord. 

To keep up this communication requires that the sensory 
and motor fibres, already described in their connection with 
the columns of the spinal cord and the brain, should be 
connected also with the gray matter of the cord ; and this 
we find to be the case. Movements made in response to 
this action of the spinal cord are said to be reflex, because 
the impression is made on 
the surface of the skin, and 
thence conveyed to the cord, 
which reflects or sends back 
the motor impulse to the 
muscles. The action is called 
reflex action. The nature of 
this movement is illustrated 
in the accompanying dia- 
gram (Fig. 85). 

The importance of having such a power assigned to the 
spinal cord, independent of the will or of sensation, is seen 
in every-day life. The rapid and involuntary manner in 
which we throw up the arm as a shield from immediate 
danger, as a fall or a blow, is an illustration in point. If 
we seize a substance that is too hot to hold, we drop it in- 
voluntarily through this very reflex action. During sleep 
the mouth will often receive and the throat swallow water 
involuntarily when placed to the lips. The body also turns 
in bed during sleep, not at all under the control of the will, 
but as a sequence of this reflex action alluded to. What 
are commonly known as spasms or fits are examples of an 
intensity of reflex action of the spinal cord. They are 
sometimes, as in lockjaw and hydrophobia, called into 
violent exercise from the slightest causes, and the action 



Fig. 85. — Simple Reflex Action. 

1, sensory surface; 2, muscle; a, sensory 
nerve; ft, nerve-cell; c, motor nerve. 
(The nervous influence travels in the 
direction indicated bv the arrows.) 



214 PHYSIOLOGY. 

of the muscles is painfully and intensely increased under 
the stimulus sent out to them from the spinal cord. 

From all these facts we learn that the spinal cord not 
only acts as a messenger between the external parts of the 
body and the brain, but that it has also an independent 
duty of its own, and effects muscular movements that are 
entirely beyond the control of the will. 

Functions of the Medulla Oblongata. — We have already 
shown that this portion of the nervous system is the con- 
necting link between the brain and the spinal cord. It 
contains a larger amount of gray matter than we find in 
the spinal cord. Its duties are chiefly to preside over the 
functions of respiration and deglutition. It is a conductor 
of nervous impressions, as the cord also is. Motor im- 
pressions — those which result in the movement of muscles 
— pass along its anterior columns. All sensory impres- 
sions — those which call up sensation in the brain — pass 
along its posterior columns. 

The fact that respiration and deglutition or swallowing 
are controlled by the medulla oblongata shows how abso- 
lutely necessary this nervous centre is to the maintenance 
of life. Experiments on animals have shown that almost 
all the brain may be gradually removed without destroying 
respiration or life. The spinal cord can also be cut away 
in animals from below upward until near the throat the 
phrenic nerve is reached, and this is the nerve distributed 
to the muscle called the diaphragm, whose rise and fall in 
respiration have already been alluded to (p. 130); but the 
moment this nerve is cut or the msdtfMa oblongata is 
touched death ensues. Paralysis would of course result 
in similar experiments on the brain or spinal cord, but not 
necessarily death. 

This portion of the nervous system is also capable of the 



THE NERVOUS SYSTEM. 215 

most important reflex actions connected with respiration, 
as is seen where, from any cause, such as lockjaw, etc., the 
muscles connected with breathing become fixed and immov- 
able and respiration is impossible. 

Functions of the Cerebellum. — The duty performed by 
this part of the brain was for a long time a puzzle to phys- 
iologists. It could only be determined by experiments on 
living animals, as may indeed be remarked of other parts 
of the nervous system. It seems to be clearly established 
that it is the nervous centre which regulates and keeps in 
order the motions of man and animals. In the experiments 
alluded to the sensation remained, but the animal could 
not move, fly, or walk, or even stand. By the action of 
the cerebellum the movements of those muscles which are 
under the control of the will are carried on harmoniously. 
The more developed the quality or variety of muscular ac- 
tion, the more developed is this organ found to be. This 
fact explains the high state of development it attains in 
man, ivhose muscular system is attended with such varied 
and complicated movements. 

The cerebellum may be briefly stated, then, to be a reg- 
ulator of muscular movements. In some of the experi- 
ments on pigeons — which seemed essential at first to estab- 
lish an important fact, but which can hardly be considered 
necessary now merely to gratify morbid curiosity — it was 
found that if the cerebrum or brain proper was taken 
away from one of these birds the animal would remain 
firm on its feet, while a pigeon from Avhich the cere- 
bellum was only partially removed would exhibit the un- 
steady and uncertain gait of drunkenness. Sensibility is 
not lost in the latter case. The cerebellum does not orig- 
inate movements, but it regulates and gives precision to 
them. This is another case in which disease or injury aids 



216 PHYSIOLOGY. 

us in our knowledge of physiology — a point on which we 
have insisted from the very outset of this work (p. 11\ 
When the cerebellum is affected in man — and this seldom 
occurs — there is always unsteady movement and a tendency 
to backward or other unusual motion. It is believed also 
that the regular movement of the eyeballs is controlled by 
the cerebellum. 

Functions of the Cerebrum. — As previously stated, the 
cerebrum or brain proper is the great organ of thought, 
sensation, and intelligence. The exercise of judgment and 
reasoning power belongs to it alone. The brain of man is 
in size and development far superior to that of all other 
animals. AYhen we come to speak of the nervous system 
of other animals than man we shall understand more clearly 
wherein this distinction lies. It may here be stated, in an- 
ticipation, that as a general rule an accurate estimate may 
be formed of the intelligence of animals by comparing the 
size of the cerebrum or brain proper with that of the spinal 
cord and the ganglia or nervous masses at its upper portion. 
Although reflex movements, such as those already alluded 
to, may be carried on for ^ome time even in animals that 
are born without a brain, and sufficient motion take place 
to sustain life, all power of voluntary motion is absent. 
How much of the brain, whether all of it or only a part, 
is necessary to effect this exercise of voluntary motion, it 
is difficult to say, for small amounts of the substance of the 
brain have been lost by accident, and yet the power has 
not been lessened in any way. It is not many years since 
an iron bar used in blasting near a New England village 
passed directly through the brain of a Avorkman without 
destroying life or very materially interfering with his move- 
ments or with the exercise of his intellect or will. 

Physiology has not yet determined what are the uses of 



THE NERVOUS SYSTEM. 217 

each separate lobe of the brain as distinct from its fellows. 
It has been suggested that it was originally divided into 
portions, rather than left to remain a single tremulous mass, 
in order to provide against the possibility of injury or disease 
of one lobe involving the whole brain-mass in general de- 
struction, and thus endangering life. It has been thought, 
at any rate, that the two hemispheres may act — that is, think 
— separately as well as together. Certainly there are moments 
in the experience of every one when the mind, seemingly 
intent on a single theme, as in reading, will Avander off to 
a hundred other fancies. Perhaps in time human ingenuity 
will be able to trace the two different lines of thought in 
which the mind then indulges to the separate hemispheres 
or the individual lobes as their starting-point. 

Let it be distinctly understood, in regard to the move- 
ments of the body, that the cerebrum originates and con- 
trols the voluntary motions or movements of the body, 
while the cerebellum is the organ which harmonizes them, 
and that reflex movements, such as those previously alluded 
to, which are excited entirely independent of the will, are 
connected with the spinal cord and the sympathetic system 
of nerves. 

It has been urged against the accuracy of our knowledge 
of physiology derived from experiments on animals, and 
by analogy applied to man, that independent of its cruelty 
and severity the loss of blood may act as a severe shock to 
the nervous system. A new plan has recently been prac- 
tised of developing responses from the brain by the action 
of electricity applied to its various parts. It was found 
that if one particular spot on the brain was stimulated the 
muscles of the neck were called into action ; if another spot, 
the muscles of the face or of the eyeballs or of the leg 
responded. Nothing is yet certain here, however ; we may 

19 



218 PHYSIOLOGY. 

hope to learn much in the future. There is a form of 
disease of the brain in which the patient finds it not only 
impossible to express his thoughts in words, but sometimes 
may employ the wrong word to express his thoughts, as 
when he wishes a knife and asks for a spoon. In such a 
case one of the convolutions of the leftside of the brain is 
usually found to be affected. 

Phrenology. — As already stated, it has been thought by 
many that the brain may be made up of a collection of 
different organs, each of which may be endowed with special 
powers or qualities. This is called phrenology (from two 
Greek words meaning " doctrine or description of the 
mind ") ; but the word is very often understood to imply 
the examination of the elevations and depressions on the 
skull, with the view of learning from them something of 
the peculiarities of mind of the individual. The attempt 
has been made to map out the surface of the skull with 
tracings upon it of mental characteristics, under the idea 
that there is some relation between them and the forma- 
tion of the cranial bones. While it is very possible that 
in time we may be able to assign functions to each portion 
of the brain, there seems little ground for believing in the 
skull as an index of its contents. 

Sleep. — It is a strange fact that the physiology of sleep 
is so little understood at this late day. We know that the 
active exercise of the brain is temporarily suspended at that 
time, and that respiration, digestion, secretion, and circula- 
tion go on as during the waking state, although not with 
the same activity ; that the object of sleep is rest, that it is 
likely to come on regularly at fixed hours, and that it can 
sometimes be controlled by the will, and is often a matter 
of habit. The amount of sleep necessary to man depends 
on the age, habit, and condition of the individual. The 



THF NERVOUS SYSTEM. 219 

very young and the very old require the most sleep — the 
younger, because the vital processes are in such a state of 
activity that rest is an absolute need ; the older, because 
they are so feeble that sleep and repose are indispensable. 
During sleep the pulse becomes slower, the number of 
respirations fewer, the breathing deeper, digestion less 
active, and a smaller amount of carbonic acid is given 
off from the lungs. The effect on the brain is to deaden 
the perceptions, to produce confusion of ideas and a loss 
of mental balance. So far as relates to the exact cause of 
sleep we are yet in the dark, but it seems to be the fact 
that there is less blood in the vessels of the brain at that 
time. Eight hours of sleep' would seem to be the amount 
which is usually required by the adult, but this will of 
course be governed by habit and other circumstances. 

When the brain becomes at all active during sleep dream- 
ing results, but such activity never occurs during profound 
slumber. It may be due to disturbances of the digestive 
organs, as after a full meal, and when exaggerated by great 
oppression from this cause may give rise to nightmare, as it 
has been called. 

Summary. — We may briefly sum up the facts known to 
us in relation to the nervous system. The nervous elements 
with which we have to deal are the two divisions of the 
nerve-substance into nerve-cells and nerve-tubes or fibres. 
The nerve-tubes serve as conductors of the nervous fluid, 
being likened in this respect to the action of electricity, 
although differing greatly from it. The nervous matter is 
of two kinds, gray and white ; the gray is found in the 
outer part of the cerebrum or brain proper and in the inner 
part of the spinal cord, and especially in the nervous masses, 
large and small, called ganglia, of which the gray matter 
forms the greater part. The white substance is found in 



220 PHYSIOLOGY. 

the interior of the brain, the outer portion of the spinal 
cord, and in the nerves. It may be stated as a rule that the 
gray matter originates impressions or actions, and the white 
matter conducts or conveys them away. 

The general nervous system is divided into a cerebro- 
spinal system and a sympathetic system. The cerebro- 
spinal system includes the cerebrum, cerebellum, medulla 
oblongata, spinal cord, and the nerves associated with them. 
The great sympathetic is a chain of ganglia beginning at 
the brain and running the whole length of the chest and 
abdomen, with nerves going off to the various organs, to 
the vessels, and to the cerebro-spinal system. The cere- 
brum, or brain proper, is the" seat of sensation, judgment, 
and intellect, and controls voluntary motion. The gray 
matter is the originator of mental power, and the higher in 
the scale the animal is, the greater the amount of this sub- 
stance. The cerebellum harmonizes the movements of the 
body. The great sympathetic nerve, by its distribution to 
the heart, the various glands and organs, brings the various 
parts of the body in sympathy with one another, and by 
its distribution to the bloodvessels changes their capacity 
and regulates the amount of blood sent to them. 

The medulla oblongata is the centre of the respiratory 
movements, and most of the cranial nerves, except those 
of sight and smell, take their origin from it or from the 
portions of the brain close to it. The spinal nerves have 
two roots — one anterior, the other posterior, — the posterior 
root containing only sensory fibres, or fibres connected with 
sensation, the anterior root only motor fibres, or fibres con- 
nected with motion. Some of the cranial nerves — those 
derived from the base of the brain — are concerned in sen- 
sation — either general sensation, such as would give rise 
to pain if injured, or special sensation, as indicated by the 



THE NERVOUS SYSTEM. 221 

senses of hearing, sight, etc. — or in motion. As the struc- 
ture of a nerve reveals to ns no difference to account for 
this variation of function, we must suppose that the gray 
matter of the brain with which the nerves communicate 
must have something to do with tin's peculiarity. 

The gray matter in the centre of the spinal cord has the 
power of originating reflex action, and of creating reflex 
movements, without calling upon the brain. General im- 
pressions are transmitted to the brain along the spinal cord 
and medulla oblongata, and the brain acts in response. The 
spinal cord, in its reflex action, regulates involuntary move- 
ments connected with the nutrition of the body entirely 
independent of the brain, and also involuntary movements 
of voluntary muscles, as when Ave throw up the arm to 
shield us from danger. It will be readily seen how much 
labor is thus saved the brain proper, which is left to the 
performance of its high duties and intellectual work, in 
many respects untrammelled by attention to minor details 
of e very-day life. 

There is very little known of the functions of the ner- 
vous masses, called cranial ganglia, at the base of the brain, 
except that they resemble the spinal cord in the fact that 
they are concerned in sensation and motion. 

The Nervous System of Animals. — Without some know- 
ledge of the arrangement of the brain, spinal cord, and 
nerves in animals lower in the scale than man, physiology 
would have been unable to reveal so much in regard to his 
nervous structure. When Ave look through the Avhole 
range of animal life, Ave find a general plan running 
through all, differing in details, according to the necessities 
of each animal. It is usual to compare man with the 
mammalia generally — that is, animals next him in the 
scale — and \vith birds, fishes, and reptiles. All these are 

19* 



222 



PHYSIOLOGY. 



constructed with the same leading parts as already de- 
scribed in man. They have a cerebrum or brain proper, 
cerebellum, medulla oblongata, and spinal cord, with their 
proper nerves, and they have a sympathetic or ganglionic 





Fig. 86. — Brain of a Rabbit. 

1 hemisphere of brain ; 2, cerebellum. 

The middle lohe of the cerebellum is 
quite large. 



Fig. 87.— Brain of a Cat. 
The convolutions are very distinct, and 
the middle lohe ol' the cerebellum is 
small. 




Fig. 88. — Brain of a Pigeon. 
A, view from above; B, lateral view of the brain, cut in half. 

A. a, olfactory lobes; b, lobes of brain ; o, optic lobes; d, cerebellum ■ e. medulla 

oblongata. 

B. a, cerebrum , b, cerebellum c, olfactory nerves; d, optic nerves; c, medulla ; 

/, spinal cord. 

system, all of which possess the properties ascribed to them 
in the human apparatus. 

The first and very important point of diiference is in 
the hemispheres of the brain. In man these attain their 
highest development. In him they are not only more ex- 
tensive, but the convolutions are deeper and so well-marked 
and numerous as to admit of a much larger amount of 
room for brain-matter. They cover completely the little 



THE NERVOUS SYSTEM. 



223 



brain, or cerebellum, and all other parts of the brain-mass 
near them ; but as we descend in the scale of animals we 
find them covering them less and less, until the cerebellum 
is seen to project decidedly beyond the cerebrum. This 
will be noticed in the accompanying illustrations (Figs. 86, 
87, 88). Other portions of the interior of the brain are 
less perfectly developed, and some parts are entirely absent. 

In the very lowest forms of animal life, such as sponges 
and the diminutive creatures in fluids which have been 
called infusoria, there is total absence of a nervous system, 
so far as we can determine. In the sea-anemone a trace of 
a nervous system is seen as a little knot of nervous matter, 
like a gano-Kon, with fibres radiating from it like nerves. 

Some insects and shell-fish, which have no spinal column, 
differ of course in the interior arrangement of the nervous 
system, ganglia or nervous 
centres taking the place of a 
spinal nervous apparatus,and 
acting as brains (Fig. 89). In 
some of those animals which 
have no spinal column — the 
star-fish, for example — there 
is a ring of nervous sub- 
stance around the oesopha- 
gus which sends off branches 
to all the rays, and this is 
its whole nervous system. 
In the mollusca — animals 
of which the oyster is an 
example — there are usually 
three ganglions, in the head, foot, and above the ali- 
mentary canal — with nerves radiating from them, in this 
respect resembling the sympathetic or ganglionic system 





Fig. 89. — Typical Forms of Nervoes 
System in Invertebrates. 

A, nervous system of a serpula, a marine 
annelide; a, cephalic ganglion. B, nerv- 
ous system of a crab ; a, cephalic gang- 
lion ; 6, mass of* ventral ganglia fused 
together. C, nervous system of an ant ; 
a, cephalic ganglion. 



224 



PHYSIOLOGY. 



of mail: They have sensation and motion and internal 
organs, all in simple degree, but sufficient to show a 
similar design running; through the animal organization. 
In insects, which as we know vary so greatly among them- 
selves in size and structure, the nervous system is not a 
constant arrangement. In all of them there is a distribu- 
tion of nerves to the organs of digestion and circulation, 
similar to the sympathetic system in man. In some of 

these little animals, which are 
made up of a series of rings 
placed one above the other, 
the nervous ganglions are 
arranged like a chain, from 
which nerves are given off. 
Some idea of the nervous sys- 
tem of these animals may be 
formed from the accompany- 
ing illustration (Fig. 90). It 
is rather a singular fact that 
all those animals which are 
devoid of a spinal column — 
invertebrate animals — have 
their nervous system along 
the under or ventral part of 
the body, as it is called (from 
venter, " the stomach "). 

In vertebrate animals— that 
is, animals which have a spinal 
column — the nervous system is along the back part of the 
body. They have, in other words, a cerebro-spinal axis, 
such as we have described in man, consisting of brain and 
spinal cord. There is not much difference between one of 
these animals and another in the arrangement of the spinal 




Fig. 90. — Nervous System of 
Insects. 

A, grasshopper; B, stag-beetle. 



THE NERVOUS SYSTEM. 225 

cord, the chief distinction being in the development of the 
brain. The hemispheres of the brain, for instance, are 
very small in some fishes, and much longer and broader in 
the tortoise. In birds (Fig. 88) the hemispheres are still 
larger, and the middle portion of the cerebellum is all that 
we see of that organ. In some animals — the rabbit (Fig. 86), 
for instance — the convolutions are almost entirely absent. 
As we ascend in the scale (Fig. 87), the hemispheres become 
still larger, the convolutions begin to make their appear- 
ance, and gradually become more numerous and deeper. 
In the dog, this increase of number and depth is very 
apparent. Of the elephant, this is still more emphatic- 
ally true. 

It is hardly complimentary to man, but it is nevertheless 
the fact, that in the chimpanzee and orang-outang there is 
noticeable a decided approach to the structure and shape 
of the human brain in the development of the hemispheres, 
proportionate size of the convolutions, etc. The brain of 
these animals is about one-fourth that of man in size. 

Such is briefly a statement of the chief facts that it 
seems necessary to impart of the knowledge thus far ac- 
quired of the structure and functions of the nervous 
system. The subject is intricate at best, and the most cul- 
tivated minds in and out of the medical profession are 
still puzzled over many undiscovered points of its physi- 
ology. Memory and language, for instance, have not yet 
been assigned their exact place, although the faculty of 
language is said by some to have its tenement in a small 
portion of the brain near the left temple. If this should 
prove to be so, we may hope in time to give to other quali- 
ties, accomplishments, and virtues " a local habitation and 
a name" in tracts of brain-substance long since explored, 
but hitherto deemed barren and desolate. The reader must 



226 PHYSIOLOGY. 

not neglect the study of the nervous system from any 
thought of its difficulties, but, like those who have pre- 
ceded him for many, many years in the search after the 
unknown, endeavor to master them by patience and study. 
He will thus acquire the amount of outline knowledge 
with which every w T ell-educated student should become 
familiar. 



QUESTIONS. 



Is a nervous system possessed by the vegetable? 
What functions belong to both plants and animals ? 
What is the object of a nervous system ? 
Is the nervous system under control of the will ? 
What is the cerebro-spinal system ? 
What are the two great nervous centres controlling it? 
What are the nerves ? 

How do we know that they are largely distributed through the body? 
What is the sympathetic system? 
What is the ganglionic system? 
What are its uses? 

What are ganglia? How are they connected together? 
Do the sympathetic nerves communicate with other nerves? Why? 
How is the gastric juice excited by sympathy? 
What two kinds of nervous matter are there? 
Which is usually found in the nerves? 
What is the appearance of the gray matter? 
Do we have the white or the gray matter in the ganglia? 
In the brain how are the white and gray matters arranged? 
Which kind of matter — the gray or white — originates nervous power? 
Which conveys it? 

What is the cerebro-spinal fluid? 

What are its uses? 

Into what three parts is the brain divisible ? 

What is meant by the words medulla oblongata? 

What is the pons Varolii, and why is it so called ? 

How much of the brain is the brain proper or cerebrum ? 

What part of the brain is the seat of intellect? 



THE NERVOUS SYSTEM. 227 

What is the average weight of the brain in man and woman? 

How does the weight vary with age ? 

What is said of the weight of an idiot's brain? 

How does the weight of the human brain compare with that of the 
elephant and whale? 

What proportion does the weight of the brain bear to the weight of 
the body in man? In the elephant? In the horse? In fishes? Jn 
birds ? 

What races have the greatest development of brain? 

How is the capacity of the skull ascertained? 

What is the facial angle? What information does it convey? 

W 7 hat are the convolutions of the brain? 

What is the chemical composition of the brain ? 

What are the hemispheres of the brain? 

How are the gray and the white matters arranged in the brain? 

How are the brain and spinal cord connected? 

What may we learn of the uses of the brain from accident or disease? 

What is the cerebellum ? What is its general arrangement? 

What is the arbor vita? of the cerebellum ? 

W T hat is the general arrangement of the spinal cord ? 

W T hat is the effect of the crossing of fibres from the cord? 

What are the nerves ? 

Of what materials are the nerves formed? 

Wliat are the uses of the nerves? 

How are the nerves protected from injury ? 

W 7 hat are gangl 



ions 



W T hat portion of the nervous system is made up of ganglions? 

W 7 hat processes or functions does the sympathetic system control ? 

Do the nerves communicate with each other in the same way that 
bloodvessels do? 

What is the cerebro-spinal axis? 

What portion is included in the skull? In the spine? 

How are these parts protected from injury ? 

With how many coats or membranes is the brain covered ? The spinal 
cord ? 

Where do the cerebro-spinal nerves come off? 

Are they single? 

How is the body divided symmetrically ? 

How many spinal nerves are there? How many cranial nerves? 

What is believed by some physiologists to be a different origin and 
course of the nerves? 



228 PHYSIOLOGY. 

How do the cranial nerves pass out of the skull? How do the spinal 
nerves pass out ? 

What organs are supplied by the cranial nerves? 

What is the nerve of smell ? Of vision ? 

What organs are supplied by the fifth pair of nerves? 

What are the uses of this nerve? 

What are the duties of the other cranial nerves? 

When several nerves are distributed to an organ — the tongue, for ex- 
ample — what different duties have they? 

What are the roots of spinal nerves? 

How are the gray and white matters arranged in the spinal cord ? 

Which is in excess ? 

Is the posterior root connected with sensation or with motion? The 
anterior root? 

What nervous body is there on the posterior root? 

What are the columns of the spinal cord? 

What effect has injury of the cord on sensation or motion ? 

What is meant by a part, as the foot, being asleep? 

Why is motion of the muscles interfered with when a nerve is cut? 

Why does the skin feel numb ? 



What is parab 



VS1S 



If the posterior column of the cord is injured, is motion or sensaiion 
interfered with? 

How does the lower part of the spinal cord terminate? 

What muscles connected with respiration are supplied with spinal 
nerves ? 

What is the muscle chiefly concerned in gentle breathing? 

How would respiration be affected by injury of these nerves? 

In what portion of the body is the greater part of the sympathetic 
nerve placed? 

What functions or processes are under control of the sympathetic 
nerve ? " 

What is the duty of the ganglia connected with this nerve? 

What action of this nerve is blushing an example of? 

Does the sympathetic system ever exist alone? 

When an impression is made on any part of the body, how is that 
impression conveyed to and from the brain? 

What are the sensations? 

What is the great central organ of sensation ? Of volition, or the 
will ? 

W T hat are the duties of the two kinds of nerves ? 



THE NERVOUS SYSTEM. 229 

What effects on sensation or motion follow if the nerves going to the 
brain or spinal cord are exposed? 

To what organs are motor nerves distributed? 

What activity does the spinal cord exhibit during sleep or when the 
brain is not active ? 

What part of the spinal cord then acts? 

What are reflex movements? 

What familiar examples of reflex action are cited ? 

What, then, are the different duties of the spinal cord? 

What is the relation of the medulla oblongata to the brain and spinal 
cord ? 

What functions or processes does the medulla oblongata preside over? 

Through what columns of this medulla do motor and sensory impres- 
sions travel ? 

W T hich is the most necessary to the life of an animal, the brain, spinal 
cord, or medulla oblongata ? 

What is the function or duty of the cerebellum? 

What has been the result of experiments on the cerebellum of animals ? 

Has the size of the cerebellum any relation to the muscular power? 

Does the cerebellum originate motion? 

What portion of the eye is regulated by the cerebellum? 

What are the functions or duties of the cerebrum? 

How does the brain of man compare with that of other animals? 

What influence has the brain over motion? 

Does injury to the brain destroy its power? 

What are the functions of the separate lobes of the brain? 

Do the two hemispheres act together or separately? 

What portion of the nervous system originates and controls the move- 
ments of the body? What portion harmonizes them? What portion 
presides over the reflex movements? 

What objection may be made to the accuracy of experiments on 
animals ? 

What is the effect of electricity applied to different points on the 
brain ? 

What is phrenology ? 

What is it usually understood to include? 

What is the condition of man and animals during sleep? 

Which of the functions go on less actively during sleep? 

What is the amount of sleep necessary to a healthy person ? 

At what ages is the most sleep required ? Why ? 

What effect has sleep on the pulse, on respiration, and digestion ? 
20 



230 PHYSIOLOGY. 

What is the state of the bloodvessels of the brain during sleep? 

What is the act of dreaming? 

What portions of the nervous system -do animals possess in common 
with man ? 

Which portion does man possess in its highest form of development? 

In the lowest forms of animal life, what evidences of a nervous system 
do we find ? 

How is the nervous system arranged in insects? 

What are invertebrate animals? Vertebrate? 

In what part of the body do we find the nervous system in the inver- 
tebrate animals ? In the vertebrate ? 

How is the nervous system of the star-fish arranged ? Of the mollusca ? 

What other peculiarities do insects present? 

What peculiarity is there in birds ? In rabbits? 

What portion of the brain becomes developed as we rise higher in the 
scale of animals? 

What animals approach man in the general structure and shape of 
their brains? 

What is the proportion which the brain of a monkey bears to that 
of man? 

By way of summary of this chapter on the nervous system : — What 
are the two kinds of nerve-matter? The functions or duties of each ? 
What portions of the cerebrum are composed of white matter? Of gray 
matter? What portions of the spinal cord are made up of white matter? 
Of gray matter? Of which kind of matter are the nerves composed? 
What are the two great divisions of the nervous system called ? AVhat 
is included in the cerebro-spinal system ? What is the arrangement of 
the sympathetic system ? What parts are supplied by it ? What gene- 
ral effect has it ? What effect has it upon the bloodvessels ? What are 
the functions of the cerebrum or brain proper? What, are the functions 
of the cerebellum? What is the function of the medulla oblongata? 
What is the arrangement of the spinal nerves ? What duties have the 
cranial nerves? What is the reflex action of the spinal cord, and where 
is it seated? How are general impressions conveyed to the brain? 
What kind of movements are regulated by the reflex action of the spinal 
cord ? What are the functions of the cranial ganglia ? 



THE SENSES. 



The Senses and their Objects. — Allusion was made sev- 
eral times, in describing the nervous system, to general sen- 
sations. It was there shown that they depended on the 
presence of a mind ; that is, of a mind conscious of the 
impressions made on the nerves of sensation. We have 
now to consider special sensations, which are generally 
known as the senses, such as touch, taste, vision, hearing, 
and smelling. These all require special organs adapted to 
their perfection. Not only nerves are necessary, but also 
in some of them a physical arrangement, such as that of 
the eye with its delicate apparatus to receive the light, 
before the nerve is at all impressed by it. The object of 
the senses is to make us acquainted with the world around 
us. Without them we should be unable to appreciate the 
properties of matter, and would have no ideas of taste, 
odor, or sound, such as we acquire through the tongue, 
the nose, or the ear. 

Cultivation of the Senses. — The five senses are not all as 
fully developed in man as in other animals. Man has his 
intellect more perfect, while in some of the other animals 
the senses, such as those of smell and hearing, seem su- 
perior to the powers of their intellects. Some of the senses, 
such as the taste, need cultivation in man, but they can be 
cultivated until they become sources of misery as well as 
of pleasure. The ear, for instance, can be trained to the 

231 



232 j PHYSIOfc*)GY. 

utmost refinement of musical tones, but may be painfully 
annoyed by the slightest discord. So, too, the eye may be 
able to distinguish the faintest colors, and yet be constantly 
distressed by hues or tints that may not be blended in har- 
mony. The most appetizing enjoyment of food and drinks 
may more than satisfy one's palate, and yet the taste may 
be cultivated to such an absurd extent that articles which 
please the fancies of almost any one else will be disgusting 
to his over-sensitive nature. 

Distinction has been made between such senses as hear- 
ing and sight, which lead to actual exercise and gratification 
of the intellect, and are therefore called intellectual senses, 
and taste and smell, which do not subserve any such high 
purposes, but are merely corporeal senses ; that is, almost 
wholly for the enjoyment of the body, without exciting or 
leaving much intellectual pleasure in their train. The nerves 
connected with the senses are not capable of performing any 
other function except that for which they were created. 
The nerve of sight can do nothing more than fulfil the 
objects of vision ; it does not, for example, give any evi- 
dence of pain ; and it may be as truly said of the nerves 
of smell and of taste that they are incapable of any other 
functions than those of assisting in the appreciation of 
odors and flavors. 

In addition to what are generally known as the five 
senses — touch, taste, smell, sight, and hearing — some phys- 
iologists describe hunger and thirst, the sense of tempera- 
ture, and other sensations, as if they were special senses. 
From the earliest times, however, the five just mentioned 
have been the only ones universally recognized as " the 
senses/' and such it will now be our province individually 
to describe them. 



TH SENSES. 233 

TASTE. 

The Organ of Taste. — Taste is really a variety of the 
sense of touch, except that the surface is that of the tongue 
and the lining membrane of the mouth, which is a mucous 
membrane, and not, as in touch, the skin or outer covering 
of the body. Taste is not perfect unless this membrane is 
also perfect, for if the latter be injured in any way pain 
will take the place of taste. The actions of mastication 
and insalivation, already referred to in digestion of the 
food, which include the share performed by the teeth and 
salivary glands, enable the alimentary mass to be brought 
in contact with the nerves of taste in all parts of the cavity 
of the mouth. The sapid qualities of different articles are 
brought out by these very acts of division and moistening 
of the food. Taste is not properly accomplished, indeed, 
unless the action of the saliva and of the teeth is well exe- 
cuted. The impression is made on the nerves of taste, and 
thence conveyed to the brain, which appreciates it. While 
the chief organ of taste is the muscular organ known as 
the tongue and the mucous membrane covering it, other 
parts of the mouth contribute their share in perfecting the 
sense. 

There are several important nerves which are sent to the 
tongue, but they do not all take part directly in the accom- 
plishment of the sense of taste. The tongue is also sup- 
plied with muscles, which allow it to be moved in various 
directions, and also to take part in mastication or chewing 
of the food in swallowing. In the use of the voice certain 
letters of the alphabet are pronounced through the assist- 
ance of the tongue, as we shall see hereafter. Taste is 
under the control of the will, being exercised actively or 
passively, according to the degree to which the muscles of 

20* 



234 PHYSIOLOGY. 

the tongue are called into play. The organ of this sense 
is very properly placed at the entrance to the alimentary 
canal as an aid to the proper choice of food. Otherwise 
much of the food that is taken into the stomach might be 
rejected by that organ. 

Papillae of the Tongue. — When the surface of the tongue 
is examined it is found to be covered 
with an immense number of fine mi- 
croscopic projections, called papillae or 
villi, some of which give it the smooth, 
velvety appearance it possesses, while 
others impart to it its roughness. It 
is in these papilla? that the delicate fila- 
ments of the nerve of taste are dis- 
tributed. The papilla? are of different 
shapes, being simple like those on the 
Fig. 91.-5STHUMAN surface of the skin, or thread-like (fil'i- 
Tongue. (Showing also form), mushroom-like (fungiform), and 
the back part of the cup _ s haped (cal'iciform). It is supposed 
c, veil of the palate: b, that the two first named are concerned 

tonsil; c, epiglottis; <t, w J t J 1 t J ie senge Q f i onc \^ f the tOllffUe, 

caliciforni oreup-shaped . ~ 

papnia? ;e, fungiform or the others with the sense of taste. 

mushroom-shaped pa- Thege ^ distributed in all parts f 
pillie ; /, filiform or l 

thread-like papilla. the tongue. The tongue is also sup- 
plied with numerous little glands, which pour out a thin fluid 
to lubricate its surface and also the interior of the mouth. 
Indeed, the tongue must be moist and the article soluble 
before perfect taste can be accomplished. Experiments 
seem to indicate that the sense of taste exists over the 
whole surface of the back part of the tongue, the under 
surface of the tip, and in a narrow band along the edge 
of the tongue, and also in a portion of the palate or back 
and upper parts of the mouth. There is no sense of taste 




THE SENSES. 235 

in the gums, in the inner surface of the lips, or in some 
other portions of the tongue. It seems that some parts of 
the tongue can appreciate salty articles while other parts 
appreciate sugars. 

Taste. — We cannot define exactly the qualities which 
make some articles of diet agreeable to the taste, while 
others are disagreeable. In old times it was believed that 
the cause was due to one general principle in the various 
articles of food, which united with other elements to con- 
stitute the difference in taste between them. This is not 
the case, however, for they can be deprived of their taste 
or sapidity, as it is called, by cooking. Boiling water 
added to tea, for instance, separates the agreeable portions. 
What gives taste to an article, therefore, must be something 
peculiar to itself, which is different from that which gives 
flavor to another article. It was even thought at one time 
that sweet taste was produced by a little round granule, 
and sharpness or acidity by a pointed one ; but this is not 
the case, for two articles of very different shape have very 
opposite tastes, and they do not lose their individual tastes 
when in solution. Solution of a substance, as in water, 
separates the particles so that they may come directly in 
contact with the organ of taste ; but taste is not dependent 
on solution, for metals held in the mouth have a peculiar 
taste of their own. 

Some physiologists have made the curious observation 
that sapid bodies have a different flavor according to the 
exact point on the tongue or the cavity of the mouth with 
which they are brought in contact. Alum, for instance, 
gives an acid and astringent taste when applied to the tip 
or extremity of the tongue, and a sweetish and not at all 
acid taste at the base of that organ ; from which it has 
been inferred that the tip of the tongue has a special per- 



236 PHYSIOLOGY. 

ception of sweet substances, and the base of the tongue of 
bitter ones. 

Writers have divided savors into a variety of kinds, as 
sweet, sour, bitter, salty, etc., yet the simple division into 
agreeable and disagreeable is perhaps as convenient as any 
other, for as a rule — with important exceptions, however — 
substances of agreeable taste are generally useful, and those 
of disagreeable taste either injurious or without any advan- 
tage as articles of food. 

While the sense of taste has its seat almost entirely in 
the mucous membrane covering the tongue, the other por- 
tions of the mouth — as already stated — are not wholly 
devoid of the feeling. Some cases in point have been men- 
tioned by writers — one, for instance, in which a child was 
born without a tongue, and yet it knew that sugar was 
sweet and other substances bitter. Sometimes the papillae 
of the tongue become completely saturated with the im- 
pression of an article that has been taken into the mouth, 
and a sort of after-taste lingers there, which prevents the 
taste of another article from being appreciated. This fact 
enables the medical man sometimes to give an agreeable 
substance to conceal the taste of one of a more disagree- 
able character with which he follows it. One who is blind- 
folded cannot, after a few moments, tell brandy or gin from 
wine or from one another if tasted in quick succession. 

Quantity Necessary. — The quantity of matter necessary 
to impress the organ of taste varies according to the sub- 
stance. An amount so small that it can scarcely be weighed 
on the smallest balance will sometimes produce a decided 
taste in the mouth. In the manufacture of beer the slight- 
est amount of some very bitter material added during the 
process will penetrate a hogshead of the liquid and produce 
a very noticeable bitter taste. On the other hand, when 



THE SENSES. 237 

sugar is added to water to impart sweetness to it, the solu- 
tion is insipid or comparatively tasteless in any quantity 
less than about 70 grains to a pint of water. 

Nerves to the Tongue. — Three important nerves are dis- 
tributed to the tongue. The fifth pair of cranial nerves, 
which is the nerve of general sensibility to the face and 
organs of sense, sends a lingual branch, which gives sensi- 
bility to the tongue and greater perfection to the taste. 
When pain is experienced in that organ it is because deli- 
cate branches of this lingual nerve are affected by some 
external cause. The glos' so-phavynge' al nerve (literally, 
" belonging to the tongue and pharynx "), which is the 
eighth pair of cranial nerves, also sends branches, and 
numerous experiments have been made to prove that this 
is the nerve of the special sense of taste. The two together 
seem necessary to perfect the sense. The hypoglossal nerve 
(literally, "under the tongue"), distributed to the lower 
part of the tongue, is a nerve of motion, which controls 
voluntary movements of the tongue, swallowing, etc. 

Cultivation of the Taste. — The sense of taste is not, like 
that of sight or hearing, one that can be educated or de- 
veloped for any good or instructive effect it may have 
upon the mind. It is more under the control of the will 
than any other sense, the muscles of the mouth being 
called into use only at the wish of the individual himself. 
It is much more acute in some persons than in others. It 
may be educated to a high state of refinement, as is shown 
in tasters of wine, who are able to distinguish with accu- 
racy the peculiar flavors and characteristics of vinous 
liquors. The taste, however, may be, so to speak, be- 
numbed temporarily by indulgence or excess in drink- 
ing. Taste is not perfect unless the power of smell is 
also perfect. If the nostrils be tightly closed, the sense of 



238 . PHYSIOLOGY. 

taste is blunted or destroyed. Many articles with power- 
ful odors have a very slight amount of taste, but they are 
rendered palatable by the very fact that they are odorous. 
Those substances which are grateful both to taste and smell 
may generally be considered as wholesome or likely to agree 
with the individual, and those which are not pleasant both 
to taste and smell as likely to disagree ; but there are of 
course exceptions to such a statement. 

National Differences of Taste. — The impressions pro- 
duced on the organ of taste are singularly variable. Much 
depends on the healthy condition of the individual, and 
sometimes on the emptiness or fulness of the stomach. In 
Greenland, fish-oils and whale-oil, which would be repul- 
sive to the tastes of Europeans or Americans, are largely 
taken as food. Many articles of diet taken with gusto in 
one part of the world cannot pass the sentinel of the organ 
of taste of other parts. Some time in the last century, 
when potatoes were first imported from America to France, 
there was universal opposition to their introduction, al- 
though recommended by the royal favor of Louis XVI. ; 
their taste was considered detestable, and it was contended 
that the most serious diseases would result from their 
general use. Previous to the year 1860 horse-flesh was 
looked on with almost universal disgust in France, but in 
the siege of Paris in 1870-1 this repugnance was overcome 
when the Parisians were compelled to resort to its use. 
The taste then acquired has survived, and it is said that 
there are now several hundred establishments devoted to 
the slaughter of these animals and the preparation of this 
kind of food. 

Organ of Taste in other Animals. — In the higher classes 
of animals the organ of taste is very much the same as in 
man. The sense is not very strongly developed in birds, 






THE SENSES. 239 

in which the tongue is generally bony or cartilaginous in 
structure and the nervous papillae are absent. The tongue 
of the woodpecker is sharp and divided like a fork, with 
which it pierces insects. The parrot uses his tongue to 
maintain a firm hold on the article he may be eating. In 
some reptiles the tongue is large and muscular. In ser- 
pents it is sharp and forked and very quick in its move- 
ments. In other animals, as the frog, it is projected with 
exceeding rapidity, to enable them to seize upon insects on 
which they feed. In the bee the tongue is like a little 
tube, which acts as a sucker through which it extracts 
juices from flowers. The tongue of fishes is often im- 
movable in the throat, and perhaps covered with teeth. 



QUESTIONS 



What are the five senses? 

What is the general arrangement of the organs connected with them? 
What is the object of the senses? 

Are the senses more fully developed in man or animals? 
What are the corporeal senses? The intellectual senses? 
Do the nerves of the senses perform any other duties ? 
What other sensations are sometimes considered as special senses? 
Of what sense is taste a variety ? 
What is the organ of the sense of taste ? 
How do mastication and insalivation assist in the taste? 
What portion of the nervous system is the organ of appreciation of 
taste? 

What effect have the muscles of the tongue? 

How is the voice influenced by the tongue ? 

Is taste voluntary or involuntary? 

What are the papillae of the tongue? 

What are the different shapes of the papillae? 

At what part of the tongue is taste appreciated ? 

What other parts of the mouth assist in the process? 



240 PHYSIOLOGY. 

What portions of the mouth are devoid of the power of taste? 

What effect has solution on the taste or quality of food? 

Into what classes may flavors be divided ? 

Is any fixed quantity necessary to produce a flavor? 

What nerves are distributed to the tongue? 

What is the function or duty of each ? 

Is the sense of taste capable of education? 

What effect has the sense of smell on that of taste? 

Are the same articles universally appreciated by the sense of taste? 

What is the arrangement of the tongue or organ of taste in the higher 
classes of animals? Jn birds? In the woodpecker? In the parrot? 
In reptiles? In serpents? In the bee? In fishes? 



SMELL. 

The Organ of Smell. — The organ of smell is the lining 
or mucous membrane of the nose, particularly its back part. 
The object of the sense is to appreciate the odorous prop- 
erties of bodies, which penetrate the interior of the nose in 
very fine particles. The delicate surface impressed con- 
tains a large number of nervous papillae. The membrane 
is continued up into the interior of the bony cavities, called 
nasal Jos' see, which are covered in front by the nose proper, 
and open behind into the back part of the throat, so that 
the air can pass freely through. This mucous membrane 
is called the olfactory membrane, because it is the essential 
part of the organ of smell, or the Schneiderian membrane, 
after Schneider, a German anatomist, who first described it. 

Each nostril is divided at its back part into three pas- 
sages, which are so narrow that when they become swollen, 
as in a "cold in the head," they allow but little air to pass 
through, and therefore give rise to difficulty of breathing. 
Two of these cavities have communication with cavities in 
the bones, so that their extent is much increased. The 



THE SENSES. 



241 



Sclineiderian membrane, which is smooth and velvety, lines 
all the cavities, and pours out mucus to keep the parts 
moistened. This is largely increased in quantity, but 
altered in quality, in "cold in the head/' forming a 
most annoying feature of that complaint. The tears 
also come down into the nose through a canal from the 
inner corner of the eye, and help to keep the membrane 
moist, as will be described under Vision. 

The Nerve of Smell. — The nerve which is supplied to 
the nose as the nerve of smell is the first pair of cranial 
nerves, which comes off from the base of the brain. After 
it leaves that organ it divides into small branches, and 
passes through openings in one of the bones of the skull, 
and reaches the nasal 
fossae, where they are 
scattered like a shower 
in fine branches over the 
upper and middle parts 
of the Schneiderian mem- 
brane (Fig. 92). To show 
what ignorance prevailed 
at one time in regard to 
the nerves, and this one 
particularly, it may be 
stated that anciently the 
olfactory nerve was sup- 
posed to be a canal 
through which the secretion of the nose was conveyed from 
the brain, in which organ the fluid was formed. The fifth 
pair of nerves — the nerve of general sensibility to the face 
— also sends its branches to the nose, and gives general 
sensibility to it, while it helps to perfect the sense of 
smell. The shape of the nose .has probably but little to 
21 Q 




Fig. 92. 



Nerves supplied to the Nasal 

Fossae. 



242 PHYSIOLOGY. 

do with the sense of smell, except that it supplies a sort 
of funnel in which to collect the odorous particles. The 
hairs at the extremity of that organ have been supposed 
to be put there to prevent unnecessary particles or insects 
from being carried into the nose with the air. As we shall 
see in the case of the eye and the ear, there is in the organ 
of the sense of smell an external arrangement to receive 
the impression and an internal one to appreciate it. The 
external or physical part in this case is the nose ; the in- 
ternal or nervous part is the olfactory nerve or nerve of 
smell. 

Odors. — It is well to reflect for a moment on the nature 
of odors, which, like the particles that give taste to bodies, 
are emanations from various substances. Odors are part 
of the composition of these bodies, disengaged from them 
by heat, light, chemical action, moisture, etc. The effect of 
moisture in this way is shown after a summer's shower in 
a garden of flowering plants. Sometimes rubbing a sub- 
stance may develop odor where it seemed to be absent pre- 
viously. To enjoy a perfect sense of smell, the organ must 
be thoroughly open, the membrane natural, healthy, and 
moist, the nerve perfect, and the brain in a state of integ- 
rity. AVlien the smell is temporarily destroyed, as in cold 
in the head, it is because the membrane is thickened and 
the nervous filaments covered, so that the odorous particles 
cannot reach a healthy surface. 

The particles that convey odor to the organ of smell do 
not always require to be placed close to the nose. The 
smell of cinnamon has been detected at a distance of two 
hundred miles from land. Paper perfumed by a single 
grain of amber was once kept by a celebrated physiologist 
for forty years without any apparent loss of odor. The 
air is the usual medium for the diffusion of odors, but the 



THE SENSES. 243 

art of the perfumer has enabled him to prepare and retain 
the most agreeable odors diffused in liquids. 

It is just as difficult to classify odors as it was in the 
case of savors. So much depends on the nervous arrange- 
ment and development of the organs of smell and taste in 
each individual that no two persons would agree abso- 
lutely in a classification. They might, for convenience, be 
divided into animal odors (as musk), vegetable (as garlic), 
and mineral (as arsenic, when burnt). It is usual, how- 
ever, to distinguish them, according to their resemblance 
to other substances, as garlicky, etc. If, however, Ave divide 
them, like the savors, into agreeable and disagreeable, we 
may run into the error of calling agreeable some that are 
exceedingly disagreeable to other persons. 

How Smell is Effected. — The exact mode in which the 
sense of smell is exercised may be summed up in a few 
words. The air containing the odor is drawn into the 
nose, sometimes forcibly, so as to carry it as far as possible 
into the nasal cavities, in which the nerve of smell is dis- 
tributed. The mucus poured out on the lining membrane 
helps to arrest the progress of the particles, so as to enable 
theni to affect the olfactory nerve. The nose, from its 
funnel shape, collects the particles and directs them toward 
the inner parts. 

Smell and Taste. — The senses of taste and smell aid 
each other, as already stated — the smell often warning us 
against putting an article into the mouth that may be re- 
pulsive to us ; but the sense of smell is not so useful to 
man as to some other animals, which depend largely on its 
exercise in the selection of their food. 

Uses of the Sense of Smell. — It has been stated by 
physiologists that we lose the delicacy of the sense of taste 
when the sense of smell is destroyed. Experiments have 



244 PHYSIOLOGY. 

been made of tasting wine with the nostrils plugged and 
\vi th the eves blindfolded, and the difficulty of deciding by 
the taste alone has been most marked. Smell can hardly 
be called an intellectual sense, although sometimes edu- 
cated for business purposes, as in the perfumer's art ; it is 
rather a corporeal sense, for it gives but little information 
to improve the mind, no matter how well developed the 
sense may be. It must not be forgotten that another 
useful purpose served by the organ of the sense of smell 
— the nose and its cavities — is in the process of respiration. 
A channel is thus oifered for the entrance of air to the 
lungs, and if there be anything offensive in the atmosphere 
the nose may sometimes act as a detective to warn the 
individual of impending danger to his health from such 
noxious influences. It is not by any means proven, how- 
ever, that bad smells and the emanations that produce them 
are necessarily causes of disease, for many places with par- 
ticularly offensive odors have never been known as centres 
of disease, and atmospheric air productive of the most 
dangerous and widespread maladies may be perfectly in- 
odorous. 

Chemical Action. — It is contended by some that, unless 
a stream of air containing oxygen passes into the cavities 
of the nostrils at the same time with the odorous particles, 
no smell will be produced ; also, that if a current of car- 
bonic acid gas accompanies the odor the effect is arrested. 
This would seem to show that there is a chemical action 
connected Avith the perfection of this sense, and that the 
presence of oxygen is absolutely necessary. 

Sense of Smell in Animals. — Animals which have the 
greatest development of the olfactory nerves are those 
which possess the strongest instincts of scent. The size of 
the nostrils and interior bones of the nose must also be 



THE SENSES. 245 

taken into account. Sharks will collect from a consider- 
able distance around a dead body thrown into the ocean. 
Some of the higher classes of animals have a much greater 
development of the sense of smell than man. Many of 
them have a much larger relative amount of surface than 
man for the purpose of increasing the extent of the olfac- 
tory or Schneiderian membrane, such as additional cavities 
and bones. Some of the more timid animals have an acute 
sense of smell, as if to protect them against attack by their 
enemies. In birds the sense is not strongly developed, 
although sometimes the part of the brain from which the 
olfactory nerves proceed may be of considerable size. Birds 
generally use their eyes more than their organs of smell in 
the search for food. In reptiles the olfactory organs — the 
cavities and membrane — are not well developed. Fishes 
seem to have a tolerably complete arrangement for smell ; 
they have nostrils opening outward, and sacs containing 
small branches from the olfactory lobe, but the water which 
they breathe cannot be renewed like the air of the atmo- 
sphere. Yet some of them have a muscular apparatus to 
keep the water in motion, and it is believed that a few of 
them, as the shark and the ray, have a power of scenting 
as well as smelling. In insects and in animals of the crab 
or lobster kind there is no perceptible apparatus for this 
sense, although it is believed that it exists. 

The scent of animals, so noticeable in the pointer and 
bloodhound, depends on their power to detect by the organ 
of smell animal effluvia, as they are called, which are the 
emanations of odorous particles given off by animals. 
These are generally dense or heavy, and are therefore 
noticed near the ground, which will account for the posi- 
tion taken by scenting dogs, the nose being applied by 
them as low as possible. The rame remark is true in re- 



246 PHYSIOLOGY. 

gard to decaying matter, the disagreeable odors of which 
are scarcely perceptible in the upper stories of the house, 
while on the ground floor they are at their strongest. The 
emanations, whatever they may be, which produce disease 
in those who lie on the earth in the swamps of tropical 
regions are a familiar illustration in point, the people 
guarding themselves from danger by sleeping: in ham- 
mocks suspended from trees. It is said that the Bay of 
Naples is so foul that upper apartments in houses in that 
city are more desirable residences than those lower down, 
and rent at correspondingly higher rates. 



QUESTIONS. 

What is the organ of smell ? 

What is the object of the sense of smell? 

What is the lining membrane of the nose called? 

How is it arranged ? 

What is the arrangement of the cavities of the nose? 

What membrane lines these cavities? 

What communication is there between the eye and the nose? 

What is the nerve of smell, and where does it come from? 

What other nerve goes to the nose? What are its duties? 

What effect has the shape of the nose? 

What are the uses of the hairs inside the nose? 

What is the external or physical arrangement of the organ of smell? 
The internal arrangement ? 

What are odors? 

In order that the sens? of smell may be perfect, what organs must be 
perfect ? 

Through what media are odors diffused? 

Into what division may odors be classified ? 

What is the process by which odors are appreciated? 

What is the use of the mucous secretion of the nose? 

How do smell and taste aid one another ? 

Is smell an intellectual or a corporeal sense? 



THE SENSES. 247 

What useful purpose does smell serve in respiration? 

What effect have oxygen and carbonic acid on the smell? 

What parts of the organ of smell increase the sense of scent in 
animals? 

What is the condition of this sense in other animals? In birds? In 
reptiles? In fishes? In insects? 

What does the scent of animals depend upon ? 

Why does a scenting dog point low down to the ground? 

What facts in regard to health or disease may we learn from these low 
emanations? 



TOUCH. 

All the Senses Modifications of Touch. — The five senses 
have all been considered by physiologists as modifications 
of the sense of touch. Smell and taste have been already 
shown, in considering the organs involved in their exercise, 
to be illustrations of this fact, for smell depends on the 
contact of odorous particles, and taste on the contact of 
sapid bodies. Vision and hearing will also be shown to 
be similarly caused by the contact of matter that cannot 
be weighed or handled any more than can the particles 
interested in the production of taste and smell. 

The Organ of Touch. — The skin affords an organ in 
which are distributed myriads of little nervous points 
called jpapil'lce. These are more numerous and more de- 
veloped wherever the sense of touch is most acute, as in 
the fingers. In the papillae of that region are also small 
bodies of fibrous tissue, closely connected with the nerve, 
and called touch bodies, which are supposed to render the 
sense of touch more acute, just as a hard corn pressing on 
a nerve increases its sensibility. All portions of the skin 
are endowed with the sense of touch, but this sense is most 
perfect in the hands. Here the papillae are said to number 
20,000 to the square inch. To appreciate fully this, organ 



248 



PHYSIOLOGY. 



of touch, it is necessary to understand clearly the arrange- 
ment of the skin itself. 

The Skin. — The skin is intended as a protection to the 
delicate parts beneath it, and also as a means of getting rid 
of certain watery and fatty matters from the system through 
the agency of glands emptying upon its surface. The outer 
layer of the skin is calied the epider'mia (from two Greek 
words meaning " upon the skin "). It is made up of cells 
differently shaped, and varying in thickness in diiferent 
parts of the body. It is thick, for instance, where it is 
subject to pressure, as in the fingers or heels, and thin over 

the lips. The epidermis is 
not supplied with nerves or 
bloodvessels, and therefore 
whatever pain may be felt in 
the skin, or whatever bleed- 
ing may occur from it from 
injury, must arise from the 
next layer of the skin, which 
is largely supplied with both 
vessels and nerves. The epi- 
dermis is perforated by nu- 
merous openings or pores 
for the passage of hairs and 
the ducts or canals of the 
sweat-glands (Fig. 93). 

The deeper layer of the skin is called variously the 
eu'tis (Latin for " skin "), cler'ma, co'rium (" the hide "), 
or true skin. It is made up of areolar or cellular tissue 
and elastic fibrous tissue ; the elastic tissue being in excess 
in parts that require great elasticity, as in the armpit, and 
the areolar tissue predominating where resistance is re- 
quired, as in the sole of the foot. It is thick, too, in the 




Fig. 93. — Surface of the Palm of 
the Hand (slightly magnified). 

I, 1, 1, openings of ducts of sweat-glands; 
2, 2, 2, grooves between the papiike of 
the skin. 



THE SENSES. 



249 



latter case, while in the eyelids it is very thin. Beneath 
the cutis is a layer of fat, which also varies greatly in 
amount in individuals, but which gives the figure its 
roundness and symmetrical appearance. 

The Papillae. — On the outer surface of the cutis are the 
papU'lte, to which reference has already been made. These 
are projections of varying size, the average length of which 
is about yj-^th of an inch and breadth 2Xo tn °f an inch. 
They are well supplied with minute capillary vessels ar- 
ranged in loops (Fig. 94). The bloodvessels, which are 




Fig. 94. — Papillae op the Skin op the Palm of the Hand (greatly 
magnified). 

1, papillae with two loops of bloodvessels; 2, papillae with a tactile corpuscle; 4,5, 
large compound papillae; 6. network of vessels beneath the papillae; 7, 7, loops of 
vessels in the papillae; 8, 8, nerves beneath the papillae; 9,9,10,11, tactile cor- 
puscles. 

derived from the arteries, are most numerous where the 
papillae are most developed and the sense of touch most 
acute. If we take the hand as an illustration, we will find 
that these arterial and nervous loops are very much more 
numerous in the papillae of the fingers or the back of the 
hand. The papillae do not always contain nerves as well 
as bloodvessels ; some of them have either one set or the 
other, but not both, but the most perfect of them possess 



250 PHYSIOLOGY. 

both. Those papillae which do not contain vessels are 
usually occupied by tac'tile corpuscles, or corpuscles of 
touch. All these structures are represented in Figs. 94, 
95, as seen under the microscope. 

Sweat-Glands (Fig. 75). — The skin, as previously stated, 
offers a medium for getting rid of a large amount of fluid 
through the sweat or perspiration. This fluid is obtained 
from the blood through the agency of sweat-glands, or 
sudoriferous glands, as they are technically called (from 
two Latin words meaning " sweat-producing "). Each gland 
is in the form of a tube convoluted, or turned upon itself, 
until it is in shape like a ball at its farthest extremity, and 
it has an outlet on the skin. The sweat-glands are very 
numerous, especially in the palm of the hand and the sole 
of the feet, where they are said to number nearly 3000 in 
each square inch of surface, or altogether in the whole body 
about 7,000,000. It is said that if all the sweat-glands in 
the body were placed end to end they would extend a dis- 
tance of more than three miles. The sweat secreted by 
these glands is not generally visible ; that is, it is carried 
off as a vapor, and is then called insensible perspiration. 
It is seen as a fluid when the amount is increased either by 
exercise or by the checking of the evaporation from the 
surface when the atmosphere is already loaded with mois- 
ture. It is then called sensible perspiration. 

The amount of sweat secreted in twenty -four hours 
varies, but it has been estimated at two or three pounds 
in that period of time. Experiments made with animals 
have shown that if the perspiration was entirely checked 
by coating them with a varnish perfectly impervious to 
air, the temperature rapidly sank, and the animal died 
from interference with its respiration, the blood not being 
properly aerated in the lungs. The importance of this 









THE SENSES. 



251 



evaporation in the maintenance of animal heat has been 
already alluded to (p. 181). 

Sebaceous Glands. — The skin is kept soft and pliable 
and is prevented from cracking or drying by the oily or 
fatty matter poured out 
upon its surface by nu- 
merous little glands, 
called seba'ceous glands 
or follicles (from the 
Latin word sebum, 
u suet "). They are 
abundant on the face 
and on the top of the 
head, in which last 
location they lubricate 
the hair ; but they are 
not found on the palm 
of the hand or sole of 
the foot, both which 
surfaces are usually 
dry. They are more 
numerous in the in- 
habitants of warm cli- 
mates, and in animals 
give off the odor which 
can be scented at a con- 
siderable distance by 
dogs. Some of the sebaceous secretion is also poured 
directly into the hair-follicles to anoint the hairs and keep 
them soft. The little dark points on the skin, of the face es- 
pecially, from which " worms," as they are called, are pressed 
out, are only the ducts of the sebaceous glands obstructed 
so that they cannot empty themselves of their contents. 




Fig. 95. — Section of the Skin (as seen under 
the microscope). 

1, epidermis; 2, dermis; 3, hair-follicles; 4, pig- 
mentary layer; 5, corpuscles of touch; 6, sweat- 
glands ; 7, fat-cells. 



252 PHYSIOLOGY. 

Hair (Fig. 95). — A hair is a much more complicated 
structure than would at first sight appear. It is divisible 
into a shaft and a root — one visible above the surface, the 
other having its origin in a follicle or sac within the skin. 
The shaft is made up of cells massed together, and differs 
in different animals. In man the shaft is solid and fibrous, 
with rough scales on its exterior. The shaft varies greatly 
in different animals, the scales being rougher in some than 
in others. 

The outer extremity of the hair is naturally conical or 
pointed. When a hair is allowed to grow to any length it 
may split into fibres like a painter's brush, which will be- 
come brittle and break off. This is not so likely to happen 
if the sebaceous matter is sufficient in quantity to keep the 
hair from becoming too dry. The root of the thicker 
hairs passes deeply into the structure of the skin. It is 
rounder and larger than the shaft. It is shaped like a 
bulb at the bottom of the hair-follicle or sac. 

The hair serves the useful purpose of protecting the 
surface of the body. It shields the head and face from 
danger of exposure to heat or cold. On the general sur- 
face of the body it doubtless helps to keep up the animal 
temperature. The eyebrows and the eyelashes certainly 
afford protection against dust or other injurious matters, 
and the hairs at the entrance of the nose and ears have a 
similar effect. 

The color of the hair is dependent upon the presence of 
coloring-matter in the cells of the hair-follicles. It seems 
to be established that in very rare cases the color may be 
suddenly changed by fright or emotion, probably from the 
action of an acid secretion rapidly and suddenly formed, 
so that the statement of the poet, that " deadly fear can 
time outgo and blanch at once the hair," is not purely a 



THE SENSES. 253 

fiction of the imagination. The number of hairs, which have 
been considered as practically beyond the power of man to 
count, have been estimated to be nearly 300 to a quarter 
of a square inch on the crown of the head of a man pos- 
sessing an average amount of hair ; rather more than 200 
over the forehead, and about 40 on the chin. A hair be- 
comes gray or white from deficiency of secretion of the 
coloring-matter or pigment. 

The nails are, like hairs, a turning in or inversion of 
the epidermis, forming a follicle or sac, to which blood- 
vessels are largely distributed. The fluid poured out be- 
comes cellular, and afterward flat and condensed. Each 
nail is inserted in a fold of the skin, which is reflected 
backward to the root of the nail, and then passed forward 
beneath its under surface, to which it is adherent. They 
aid in the sense of touch, and also give a firm base of 
support for the extremities of the fingers. All the ar- 
rangements connected with the skin which animals possess 
for their comfort or protection, such as horns, feathers, 
hoofs, scales, bristles, etc., are varieties of the same general 
structure as the nails, only differing in the minor details 
of the mode in which they are constructed. 

Color of the Skin. — The color depends on the deposit of 
a coloring-matter or pigment in the cells of the deeper 
layer of the epidermis. On its character and amount 
depends the difference of hue between the races. Black 
pigment is secreted in the negro, red in the Indian, etc. 
The differing fairness of skin in individuals of the same 
white race is connected with the amount of pigment so 
deposited, Freckles are nothing more than an increase 
of coloring-matter irregularly deposited. A person in 
whom the coloring-matter is entirely absent in the skin, 
hair, or the eye is called an albino (from albus, u white"). 

22 



254 



PHYSIOLOGY. 



The Hand. — This is in man the principal organ of touch. 
To assist in the exercise of this sense it is constructed in 
such a way as to be perfectly flex- 
ible, and by its variety of move- 
ments to adapt itself to the shape 
of the substance held within its 
grasp. In an instant it acquires 
appreciation of form, weight, con- 
sistence, etc. The joints between 
its numerous bones and the ten- 
dons which pass to every part of 
the hand (Fig. 96) admit of great 
variety of motion, and the thumb, 
which acts as a sort of opponent 
and at the same time an assistant 
of the other fingers, is a special 
and distinguishing characteristic 
of man. The hand lias always 
been regarded as one of the most 
valuable instruments which the Creator has given to the 
human race. 

The Sensation of Touch. — The sensation differs with the 
character of the body touched, and with other agencies, 
such as the temperature. The sensation given by differ- 
ence of temperature is not, however, to be considered purely 
a form of touch. Bodies of the same temperature, such as 
a stick or a stone, may give rise to greatly varying sensa- 
tions of touch, or, as they are generally called, tactile im- 
pressions. Softness, hardness, smoothness, and roughness 
all enter into consideration as elements. The sensation 
endures for a little while after the removal of the body 
or substance that caused the sensation. If we touch two 
points on the skin at the same time, two different sensations 




Fig. 96. — Anatomy of the 
Human Hand (back part). 






THE SENSES. 



255 



may result, but if the two parts touched are very close to- 
gether there may be only one sensation. Some physiol- 
ogists have, by means of the points of compasses applied 
to various regions of the body, determined the existence of 
the greatest diversity in their sensitiveness. At the tip 
of the finger the double sensation was found to be expe- 
rienced at the distance of only one-twentieth of an inch, 
while in the middle of the back it was only perceptible 
at a distance of rather more than two inches. 

One would think that no deception could occur in regard 
to our knowledge of the exact point that has been touched. 
A familiar illusion, however, well known from times as far 
back as the days of the old Greek philosophers, is the ex- 
periment of placing a marble between the fingers, as in 
Fig. 97, and having the sensation of one marble imparted, 
and afterward of crossing the index and middle fingers 





Fig. 97. — A Tactile Illusion. 



(Fig. 97), and having the sensation of two marbles. A 
separate impression is here made on each finger in spite 
of the knowledge that only one marble is placed there. 
When the outer skin — the epidermis — is thick, the sense 



256 PHYSIOLOGY. 

of touch will be blunted, but quick and delicate when that 
coat is thin. If the epidermis did not exist touch would 
be replaced with the sensation of pain, and things that are 
now handled with impunity would be rapidly absorbed, 
and in many cases with poisonous effects. Like the other 
senses, touch may be educated or improved by proper ex- 
ercise until it acquires the highest degree of refinement and 
delicacy, as is well seen in the execution of artistic work- 
manship. As has been well remarked, the educated touch 
of the surgeon is an instance of an acquired power of com- 
bining sensations of contact and of pressure, as indicated 
by the amount of resistance, and of forming a rapid and 
accurate judgment. 

Sense of Touch in Other Animals. — This varies greatly 
and according to their needs. In most of the higher classes 
the tongue, lips, and snout are the chief organs of touch. 
In all of them it is placed near the surface as a guard and 
protection. In many of the insects the outer covering of 
the body is thick and shell-like, but they have near the 
mouth prolongations called feelers, which are very movable, 
and can be directed toward an object or toward the ground 
on which they walk. Bats possess these in a remarkable 
degree, and are aided by them in their rapid flights. The 
scales of fishes doubtless interfere greatly with their sense 
of touch. The whiskers of the cat and of other animals 
are generally in contact at their inner extremity with a 
branch of a nerve, and thus the impression derived from 
any body they may touch is communicated to it. In some 
experiments made with cats, blindfolded for the purpose, 
it was found that these animals could find their way readily 
out of labyrinths in which they had been placed, provided 
their whiskers were left intact, but that they were totally 
unable to do so when the whiskers were removed. 



THE SENSES. 257 



QUESTIONS. 

Of what sense are the other senses a variety? 

What is the organ of touch ? 

What are the papilla?? 

What are the touch-bodies? 

Is the sense of touch confined to any portion of the skin ? 

What is the use of the skin? 

What fluids are separated through the skin? 

What is the outer layer of the skin called? How is it arranged? 

Is the epidermis supplied with vessels and nerves? 

What are the openings or pores of the skin intended for? 

What other names are given to the next layer of the skin ? 

Of what two kinds of tissue is it composed ? 

Which of these tissues is in excess in the sole of the foot? 

What kind of tissue gives natural roundness to the figure? 

Where do the papilla? arise? What is their size? 

How are bloodvessels arranged in connection with them? 

In what part of the hand are the papilla? most numerous? 

If the papilla? do not contain bloodvessels, what other bodies take 
their place? 

From what source is the sweat derived ? 

W T hat is meant by the word " sudoriferous" ? 

What is the general arrangement of the sweat-glands? 

In what parts of the body are they most numerous? How many are 
there in those regions ? 

How many such glands are there in the body? 

What is the difference between sensible and insensible perspiration? 

What is the amount of sweat secreted in twenty-four hours? 

What is the effect of completely covering the surface of animals with 
varnish ? 

What are the sebaceous glands? 

What kind of secretion do they pour out? 

Wliat effect have they upon the hair? 

In what portions of the body are they absent? 

Into what parts is a hair divisible? 

What change takes place in a hair after it becomes long? 

What useful purpose do the hairs serve? 

What effect have the eyebrows and eyelashes? 

What is the color of the hair dependent upon ? 

What does sudden blanching of the hair depend upon ? 
22* R 



258 PHYSIOLOGY. 

What is the number of hairs on different parts, as the crown of the 
head, the forehead, and chin ? 

Why does hair become white? 

What are the nails? How are they formed? 

What are their uses? 

What other parts of animals are similarly formed? 

What does the color of the skin depend upon ? 

What does the color of the races of mankind depend upon ? 

What are freckles? 

What is an albino? 

What portion of the body is the chief organ of touch? 

What qualities has it for the purpose? 

Which one of the five fingers is characteristic of man ? 

With what circumstances does the sensation of touch vary ? 

What is meant by tactile impressions ? 

By what experiments can we prove that some parts of the body are 
more impressible than others? 

What deception in regard to sensation is there in the experiment with 
a marble? 

What effect on touch has the thickness of the epidermis? 

If the epidermis did not exist, what would be the result? 

What are the chief organs of touch in the higher animals? 

What are the feelers of insects? 

What useful purpose do the whiskers of animals serve ? 



VISION. 

Importance of the Sense. — There is perhaps no organ of 
the body which is the source of so much pleasure and in- 
struction as the eye. To it we are indebted for a thousand 
enjoyments and advantages. By means of the vision Ave 
are able to appreciate light and color, and to recognize the 
form, size, movement, distance, and general properties of 
objects around us. The eye has always been a subject 
of curious study, for it is an organ founded on scientific 
principles, perfectly adapted for the duties it has to per- 



THE SENSES. 259 

form. A distinguished physicist has remarked that it is 
so perfect, so unspeakably perfect, that the searchers after 
tangible evidences of an all-wise and good Creator have 
declared their willingness to be limited to it alone, in the 
midst of millions, as their one triumphant proof. 

The Organ of Vision. — The sense of vision is dependent 
on the optic nerve — which we have seen to be the second 
pair of cranial nerves coming from the base of the brain — 
and a complicated arrangement for the transmission of 
light to this nerve. In addition there are muscles which 
move the eye in various directions, and various parts which 
are intended chiefly for the protection of that organ. The 
parts essential to sight may be said to be contained in the 
globe or ball of the eye, besides the nerve of vision and the 
brain itself, both of which must also be perfect. It is not 
neeessary for us to dwell at any length on the minute struc- 
ture of the eyeball, as it is a matter of careful anatomical 
study beyond the object of this work. It is composed of three 
coats or coverings — the first fibrous, the second vascular, 
and the third nervous — and of media that refract the light 
according to physical laws. The optic nerves as they pass 
from each side to the eyes mingle with one another like the 
letter X. This interchange of fibres of the nerves has some- 
thing to do with their harmonious action, and probably with 
the sympathy existing between them both in health and 
disease. 

Protection of the Eye.— The parts that act as guards and 
protectors of the eye are the eyelids, eyelashes, and eye- 
brows, with their thick skin and hairs, all of which shield 
it from excessive light and prevent dust from irritating it, 
while the tears and the sebaceous matter constantly poured 
over the front of the eye keep it moist and readily movable. 
These actions are examples of an involuntary kind, of work, 



260 



PHYSIOLOGY. 



such as was described under the Nervous System as being 
controlled partly by the sympathetic system of nerves and 
partly by the reflex action of the cerebro-spinal system. 
The Tears. — The tears are secreted by a gland called the 

lach'rymal gland (from 
lac>ryma, "a tear"), one 
on each side, seated 
above the outer part of 
each eyebrow (Figs. 98, 
99). We are all familiar 
with the act of weeping, 
which is simply an ex- 
cessive secretion of fluid 
from the lachrymal gland, 
usually under the influ- 
ence of emotion, but we 
are not so familiar with 
the fact that the tears are 
a'.so being secreted at 
every moment of our 
lives. 

The tears keep the sur- 
, c . . face clear and transparent. 

1,2,3,4,0, muscles ol the eyeball; fi, lachry- l 

mai gland; 7, 8, 9, ducts of the lachrymal One can easily imagine 

how devoid of lustre the 
eyes would otherwise be. The fluid thus secreted or sep- 
arated — the tears — is poured over the front of the eye by 
the movement of the eyelids, and afterward passes into the 
inner corner of the eye, into the opening of a little canal, 
which conveys it into the nose. The mouth of this canal 
can be seen as a little point in the corner of the eye next 
to the nose. The tears, being secreted at the outer part of 
the eye, and emptied at the inner corner into the nose, are 




Fig. 9S.— Thr Eyk. (The section slows 
the position of the lachrymal gland and 
of the muscles of the eyeball. 1 



THE SENSES. 



261 




Fig. 99.— The Eye. 
a, opening of canal for passage of tears into the 
nose; b, iris; exposition of lachrymal gland ; 
d, pupil; e, conjunctiva. 



compelled to travel over the whole front of the eye. The 
perspiration from the 
forehead is prevented 
from running into the 
eye by the eyebrows 
catching it and detain- 
ing it. 

The Orbits. — The eye- 
ball is also protected 
from injury by being 
placed in a deep bony 
cavity — the socket, as it is 
generally called — which 
is a hollow space pro- 
vided by nature for this purpose, partly in the frontal bone 
and partly in the bones of the nose and cheek. The 
frontal bone is that which forms the forehead in man 
(Fig. 1). The term orbit is also applied to the socket. 
The sides of the orbit project beyond the eyeball itself, 
and in this way serve as a means of protection against 
injury from force applied in any other direction than di- 
rectly in front of the eye. There is a certain amount of 
fat in the orbit which furnishes a cushion on which the 
delicate eyeball rests. It is said that this bed of fatty 
tissue is never entirely absent even in extreme emaciation. 

The Eyelids. — The eyelids are like a curtain to the eye, 
movable at will or involuntarily under the influence of ap- 
propriate muscles, the upper lid being larger and more free 
in its motions. They are covered on the outside by skin, 
but on their inside are lined by the same kind of membrane 
which lines the cavities of the body — mucous membrane — 
which is here, however, much more delicate, and is reflected 
over the front of the eyeball. In this position it is called 



262 PHYSIOLOGY. 

the conjunctiva, because it forms a kind of connection 
between the eyeball and the surrounding parts. It is a 
very sensitive membrane, and is frequently inflamed by the 
presence of dust or fine particles received into it from the 
air. It protects the eye, however, by its sensitiveness to 
such foreign bodies, for it makes a strong effort to get rid 
of them by bathing them with increased and sympathetic 
moisture of the tears and by the involuntary increase of the 
muscular action of. the lids. 

The Eyelashes. — The eyelashes collect the dust that might 
otherwise fall upon the delicate surface of the eye, and with 

the lids regulate the amount of 
light that would inevitably im- 
pinge with full force upon that 
organ. In close connection with 
the eyelashes are numerous little 
sebaceous glands (Figs, 99, 100\ 

Fig. 100. — Glands of alkibomius _ & \ & > > 

(slightly magnified). The little which pour Ollt a thick Oily 
openings back of the lashes are fl iu \l w fth which the edgCS of 

the lids are greased so that they 
do not adhere to one another. They also prevent the tears 
from overflowing the cheek instead of running into the eye 
to keep it moist. The arrangement of these little glands 
with their duets is well shown in Fig. 100. They are 
called the Meibo'mian glands, after Meibomius, who first 
described them. 

Transparent Parts of the Eye. — These may be clearly 
understood by reference to Fig. 101, which represents a 
section of the eyeball made in such a way as to exhibit 
clearly all the portions of which it is composed. The front 
and convex part of the eye, through which light must first 
pass, acts like a window to this organ, and is called the 
cur'nea, from its resemblance to horn (comu, " horn "), 




THE SENSES. 



263 



(Fig. 101, 1). Behind this is the anterior chamber (or front 
apartment) of the eye, as it is generally termed, containing 
a 'few drops of a watery fluid called the aq'ueous hu'mor 
(Fig. 101, 2). Behind this organ is a remarkable structure, 
the only solid part, called the crystalline lens (Fig. 101, 5), 
which is convex on both its front and back surfaces and 
arranged in layers like an onion. 

Farther back in the eye than the lens is another semi- 




Fig. 101. — Thk Eyk. (A vertical section through the middle of the eyeball.) 

1, cornea; 2, aqueous humor; 3, pupil; 4, iris; 5, lens; 6, ciliary processes; 7, canal 
around the lens; 8, sclerotic coat; 9, choroid ; 10, retina; 11, vitreous humor; 12, 
optic nerve; 13, 14, straight muscles of the eyeball; 15, muscle that raises the 
upper eyelid; 10, upper eyelid; 17, lower eyelid. 



fluid, transparent, gelatinous material, filling up the greater 
part of the eyeball, and called the vWreous humor, because 
it resembles melted glass. This humor is placed in the 
posterior chamber (or back apartment) of the eye, and 
occupies about two-thirds of the eyeball. All these lenses 
or media for the transmission of light, whether they be 
horny, watery, gelatinous, or glassy, form when combined 



264 PHYSIOLOGY. 

a beautiful optical apparatus without a single defect in its 
construction. 

Coverings of the Eye. — The transparent portions of the 
eye, just described, are embraced in three distinct coverings 
or coats, placed v one within the other. The outer coat, 
giving shape to the eye, is called the sclerot'ic (Fig. 101, s), 
on account of its hardness (from a Greek word, meaning 
"hard"). This is a strong membrane, and supports the 
other delicate structures of the eye. The next is the choroid 
(Fig. 101, 9), a black, opaque membrane, with numerous ves- 
sels permeating it, and having pigment-cells connected with 
it to absorb unnecessary rays of light, and thus prevent con- 
fusion of vision. The third and last membrane, the ret'ina 
(Fig. 101, 10), lines the back part of the eyeball, and is placed 
between the choroid and the vitreous humor. The retina 
is an expansion of the optic nerve, and is therefore the 
membrane which is sensitive to the action of light. In 
order to reach this membrane light must pass through the 
following transparent media: the cornea, aqueous humor, 
crystalline lens, and vitreous humor. In the front part of 
the choroid is a contractile structure, like a curtain, called 
the i'ris (Figs. 99, ft, 101, 4), a movable diaphragm, with cir- 
cular and radiating fibres, which dilate and contract the pupil, 
as the opening in the centre of the iris is called (Figs. 99, d, 
103, 3). The pupil is the central opening, if we may so call 
it, of the eye, visible in looking into any one's eye while stand- 
ing directly in front of him. The amount of light sent to 
the eye is regulated by this action of the pupil— or "apple 
of the eye," as it was formerly called — as all unnecessary 
light is shut out, and rays of light that strike on the eye 
outside the line of vision are arrested. This action is not 
under the control of the will, but is regulated by the 
reflex action of the nerves, according to the intensity and 



THE SENSES. 265 

amount of light striking upon it. This is particularly 
noticeable in going from a dark to a light room, the pupil 
gradually contracting to accommodate itself to the light. 

The Cornea (Fig. 101, 1) is quite a prominent feature of 
the front of the eye, and is in shape like the crystal or 
glass of a watch, and only about Jg-th of an inch thick. It 
has no bloodvessels supplied to it. The Sclerotic is what is 
familiarly called the "white of the eye," an exceedingly 
strong membrane which gives attachment to the muscles 
outside the eyeball that control the movements of that 
organ. The optic nerve passes through an opening in its 
back part. 

The Choroid is a very different membrane, being soft, 
delicate, and dark in color, and fully supplied with blood- 
vessels. Allusion has already been made to the dark layer 
of pigment-cells in the choroid coat, the uses of which are 
the absorption of rays of light after they have penetrated 
the transparent media of the eye. Telescopes of human 
construction are made on a similar plan, the interior of the 
tube being coated with some thick black material which 
absorbs superfluous rays of light, and thus prevents confu- 
sion. For a similar reason the eyesight of the albino, in 
whom this dark layer of the choroid is absent, is confused 
and imperfect, especially in the sunshine or in any other 
bright light. The iris (literally "a rainbow") is the part 
of the eye which gives to different persons the color — as 
blue, hazel, gray — that distinguishes them. The size of 
the pupil, or central opening of the iris, has much to do 
with the brilliancy of the eye, in young persons especially, 
for the light reflected from the front of the crystalline lens 
will then have more field for its display. The pupil is 
sometimes made to dilate artificially by the surgeon under 
the use of belladonna or some other drug, chiefly that he 

23 



2CG PHYSIOLOGY. 

may have a greater amount of space in which to apply his 
instruments. 

The Retina is a thin, smooth, and delicate grayish or 
grayish-white membrane, made up of the filaments of the 
optic nerve. It is not sensitive to any other impressions 
than those of light. A blow on the head or over the eye, 
which would give rise to pain and suffering in the other 
coats of the eye, might only produce Hashes of light or 
confused images like sparks, as they are popularly called, 
from the retina. There is a point on the retina, just at the 
entrance of the optic nerve (Fig. 101) at the back of the 
eyeball, which is wholly insensible to the action of light. 
This is sometimes called the "blind spot" of the retina. 

The Crystalline Lens lies in the front part of the eye, 
behind the iris. It is enclosed in a membrane called a 
capsule, and is held in place partly by surrounding struc- 
tures and partly by a delicate ligament. It is about a 
quarter of an inch thick, and is convex on both its front 
and back faces. Its position is well represented in Fig. 101. 
It is perfectly transparent, and when this transparency 
becomes lessened or lost, a condition called "cataract" re- 
sults, especially in old persons, which often requires sur- 
gical relief. 

The Motions of the Eyeball. — The muscles which move 
the eyeball are of course placed on the outside of that 
organ (Fig. 98). There are six of these muscles, four of 
which are straight and two oblique. Their action is con- 
fined to the rolling and turning of the ball ; they do not 
ordinarily have any power to pull it inward or to project 
it outward. The line of vision is of course varied by such 
movements of the eyeball, and if necessary the head is 
also turned toward an object when the action of the 
muscles on the eyeball is not sufficient. Usually these 



THE SENSES. 267 

movements of the eyeball take place without any con- 
sciousness of their action being aroused. Through the 
agency of these muscles the axis of vision can be turned 
in a horizontal plane of 60° toward the nose, and 90° out- 
ward, making a total of 150°. It can turn upward through 
an angle of 50°, and downward 70°, or 120° altogether. 

Light. — The true cause of luminous sensations, as they 
are called, is the action of light on the retina, which is the 
expansion of the optic nerve. Light is known more from 
its effect than as being a tangible body which we can grasp 
and weigh, like bodies that are associated with the sense 
of touch. The theory that explains most fully the laws 
of light is that which supposes the existence of an elastic 
medium occupying all space, which is excited into rapid 
waves or undulations by the sun or any other luminous 
body. The theory is hence called the modulatory theory 
of light. The waves are propagated at an almost incom- 
prehensible rate — nearly 190,000 miles a second being its 
estimated degree of rapidity. At this rate the light of the 
sun takes over eight minutes to reach us. The reception 
of these waves by the eye causes the sensation of light in 
that organ. 

. It Avill be found, in studying the principles of sound, so 
far as they are related to the organ of hearing, that a simi- 
lar theory of sonorous vibration of the air is supposed to 
produce sound. This statement is sufficient for us, in the 
study of the physiology of the eye and ear, without enter- 
ing more deeply into scientific explorations which do not 
at this time concern us. 

Sight may therefore be said to be the effect of the move- 
ment of light on the retina, exciting the fibres of the optic 
nerve, the stimulus being conveyed to the brain for its 
appreciation. As a matter of curiosity, beyond our com- 



268 



PHYSIOLOGY. 



prehension or our keenest conception, it may be briefly 
stated that at the lower end of the scale the sensation of 
red is produced by 435 billions of impulses or vibrations 
per second, and at the upper end of the scale the sensation 
of violet is produced by 764 billions of vibrations per 
second. 

Reflection and Refraction of Light. — When light passes 
through a transparent medium of unvarying density, like 
the air, it proceeds rapidly in a straight line without being 
broken in its course. If, however, it comes in contact with 
any other transparent body of different density, it is either 
reflected — that is, turned back again in its course — or it 
passes through that medium in a different direction, being 

broken or ref meted. The 
processes are called reflec- 
tion of light and refrac- 
tion of light. 

If, for instance, ab be a 
transparent substance, as 
a pane of glass, a ray of 
light, cd, will pass di- 
rectly through without 
undergoing any change. 
The ray ef, however, instead of passing directly through, 
will be bent in the direction eh. If the ray ef had passed 
from a dense medium into a rarer one it would have taken 
the direction eg. This represents the refraction of light, 
which becomes so important a consideration in the study 
of the physiology of the organ of vision. 

When the rays of light strike upon the eye they pass in 
the first place through the cornea, which is convex, and 
therefore refracts them or turns them slightly from their 
course. They next pass through the aqueous humor, which 




Fig. 102. — Refraction of Light. 



THE BEKSES. 269 

is not sufficient to cause much change in the direction of 
the rays. They next strike upon the iris, which reflects or 
turns back those which impinge upon its surface, and only 
those rays which pass through the pupil, or central open- 
ing of the iris, reach the true organ of vision at the bottom 
of the eyeball. 

It may be stated, in passing, that the color of the eye 
depends on the reflection of the light effected on the sur- 
face of the iris, or rather on the color of the choroid coat 
beyond the iris, seen through the latter. Dark eyes, for 
instance, are dependent on the deep color of the choroid as 
seen through the iris ; light eyes, on a pale and colorless 
choroid similarly seen. When the light passes through 
the pupil the amount going to the retina may be dimin- 
ished, as already stated, by the contraction of the iris 
diminishing the size of the pupil. This contraction in 
too intense a light, or the dilatation of the pupil when the 
light is not sufficiently bright, is dependent on a reflex sen- 
sation excited by the retina when impressed either with 
the excess or deficiency of light. 

The rays of light, which Ave had traced as far as the 
pupil of the eye, next come in contact with the crystalline 
lens. A reference to Fig. 101 will show very clearly the 
regular order in which these organs are placed in the eye, 
and will enable the reader to follow closely the coarse 
of the rays of light in traversing that organ. The lens 
has decided refracting power, due to its double convex 
shape, resembling that of a small bean, and to the fact that 
the layers into which it may be divided increase in density 
toward the centre of the lens. The consequence is that the 
rays of light are still farther refracted from their course, 
and when they emerge from the lens and pass through the 
vitreous humor they converge on a small space on the 

23 * 



270 



PHYSIOLOGY. 



surface of the retina, producing an image upon it of the 
object. 

The Image on the Retina. — By reference to Fig. 103 the 
convergence of the rays just alluded to will be understood, 
but it will be noticed also that the image impressed on the 



Fig. 103. — Formation of ax Image on the Retina. 



retina is reversed. The candle, instead of being in the nat- 
ural upright position, as at DE, is seen at ed as it appears 
on the retina, with the flame downward. Notwithstanding 




Fig. 104. — Inverted Image on the Retina shown in the Bullock's Eve. 

this inversion of the image, we see the object in its natural 
position. It has been supposed that the reason the image 
is not seen upside down is because during infancy the sense 
of sight is slowly and gradually educated, and that the 
child thus acquires a proper appreciation of the shape, size, 



THE SENSES. 271 

and distance of objects. It is the brain, after all, and not 
the retina, which appreciates the existence of an image, 
although images must be constantly formed on the retina 
without the brain taking any note of them. Habit and 
comparison aid the brain in arriving at a proper conclusion 
as to the position of bodies at which the eye is looking. 

Two Images Seen. — Each eye sees the same object at the 
same time; there must consequently be an image received 
by both eyes at once, and yet it is only appreciated as a 
'single object. These two images are identical both in size 
and color and in every other particular ; and when the 
retina transmits the two images of the same object to the 
optic nerve, and the optic nerve to the brain, the brain 
confounds the two in one and sees but one object. Per- 
haps the crossing of fibres of the two optic nerves, pre- 
viously alluded to, may have something to do with the 
uniting of these two impressions. 

Accommodation of the Eye to Distance. — As the eye is 
capable of seeing bodies at almost incalculable distances, 
some mechanism must exist for its adjustment for near and 
distant objects. In the natural condition of the healthy 
eye parallel rays (Fig. 105, a) coming from a distance are 
brought to a focus, or central point (x), on the retina. 
When the rays do not come accurately to a focus there, 
the image is quite indistinct, just as it is when an object is 
held so close to the eye that the refractive media of the eye 
cannot focus it on the retina. Other forms of eye exist 
in which no such accurate focusing takes place as in the 
healthy eye. In the short-sighted or myop'ic (" mouse-eyed ") 
eye (Fig. 105, b) the parallel rays are brought to a focus (x) 
in front of the retina. To ensure distinct vision the object 
must be brought near the eye, so as to allow the divergent 
rays to be focused on the retina. In the hypermetropic 



272 



PHYSIOLOGY. 



(from three Greek words meaning "beyond the measure of 
the eye"), or far-sighted eye (Fig. 105, c), the parallel rays 

of light are brought to 
a focus (x) behind the 
retina, so that it is ne- 
cessary to hold the ob- 
ject far off in order t » 
enable the less divergent 
rays to reach the eye. 
Different kinds of glasses ' 
must be used to correct 
the defects of the short- 
sighted and the far- 
sighted eye. The myopic 
or short-sighted eye may 
be corrected by using con- 
cave glasses, which will 
remove the focus farther 
back to the retina. The 
far-sighted eye (some- 
times called the presbyop' ic eye, meaning ( ' the eye of an 
old person ") may be corrected by convex glasses, which 
will bring the focus farther forward. 

After a great deal of discussion on the subject, physiol- 
ogists generally have come to the conclusion that the power 
of accommodation of the eye to distance is due to a change 
in the curvature of the front face of the crystalline lens. 
It is supposed that the lens in ordinary vision is flattened 
in front by the pressure of its capsule or covering, but that 
during the period of accommodation of the eye to distance 
the radiating fibres of a small muscle, called the ciliary 
muscle, pull on this capsule so as to relieve its tension, and 
the lens is then projected forward by its own elasticity. 




Fig. 105. 
A, natural sight; B, short-sight; C, far-sight, 



THE SENSES. 273 

Impression on the Retina. — An impression made on the 
retina is not always momentary, but may last for a while 
after the cause, as a light or bright object, has been re- 
moved. After the retina has been in the dark for a while 
it is more excitable, and of course after being exposed to a 
bright light for a while it is much less excitable. In other 
words, it is much more active after taking rest. An im- 
pression on the retina generally lasts from yg-th to ^-th of 
a second. An electric spark, which is itself of very short 
duration, may make so powerful an impression on the 
retina, and it will remain so long, that the spark will be 
visible. To show how persistent the impression is, it is 
only necessary to take a round piece of card having one 
side black and the other white, and rotate it, when only 
continuous dark bands will be seen. If a red spot be 
painted on the face of the disc it will appear, when the 
latter is rotated, like a red band, showing that the impres- 
sion made by the spot is continuous. Each impression 
made upon the retina is here confounded with those which 
rapidly follow it. Another method of exhibiting the fact 
of this persistent sensation is by gazing steadily for a mo- 
ment or two at a bright light, then looking at once into a dark 
room, when the image of the bright light will be distinctly 
seen. This shows that the original image has not yet faded 
from the retina. Several well-known toys are based upon 
this principle, one called the wheel of life, or the thauma- 
trope, being familiar to almost all. A ready mode of illus- 
trating the same effect is in the rapid whirling of a stick 
lighted at one end, which appears like a ring of fire. 

A peculiar effect of vision is what is known as irra'dia- 
tion, which is shown in Fig. 10G. The dark square in the 
white ground seems to be smaller than the white square in 
the dark ground, whereas they are of equal size. The only 

s 



274 PHYSIOLOGY. 

explanation of this impression on the retina is that in vision 
the borders of the white surface advance and encroach on 
the dark ground. It is not easy to say why, but possibly 




Fig. 10fi. — Irradiation. 

a shadow which lias tha effect to diffuse the white surface 
forms around its edge, so as to make it appear larger. 

There is one spot on the retina, called the blind spot, at 
which no sensibility to light occurs. This is at the en- 
trance of the optic nerve, and there is also at the same 
point insensibility to color. This fact is illustrated by the 

following experiment (Fig. 107) : 
™ ® Shut the left eye ; with the right 

Fig. 107.— Experiment in re- eye look steadily at the cross, 

SARD TO THE "BLIND SPOT." ^ ^ moye ^ ^ fo^g^ 

the eye and away from it. It will be found that the round 
spot will soon disappear, and it does so when the image 
from it falls directly on the entrance of the optic nerve. 
It is said that this blind spot, although small, is larg? 
enough to cause a human figure to disappear at a distance 
of about six and a half feet. 

There is a yellow spot in the centre of the retina which 
is very sensitive to light. When we take up a book to 
read and run our eyes along the line, we do so with the 
view of bringing each word, as it comes in the text, opposite 
the yellow spot. This may be regarded as the centre of dis- 



THE SENSES. 2lb 

tinct vision, the field of which is not therefore very large. 
When we look at any objects whatever, their images are 
impressed on this limited field, and are rapidly mingled 
together, so that the brain appreciates them as a whole. 
Perception of Colors. — In addition to the appreciation 
of light, the eye has also another duty to perform in the 
perception of color. There are seven elementary colors — 
violet, indigo, bine, green, yellow, orange, and red (remem- 
bered by the word " vibgyor" in which the first letter of 
each color is found). How early in life this sensation of 
color occurs is not definitely known, as we can learn 
nothing from the lips of infancy as to its personal ex- 
perience. The blind from birth, when restored to light at 
an adult period of existence, require time before they can 
appreciate distinction of color. Some persons cannot dis- 
tinguish colors at all, but only light and shadow. This 
rarely happens, however, the principal form of color-blind- 
ness being an inability to tell one color from another. Red 
and green seem to be the colors most frequently confounded. 
Red, blue, and yellow are mistaken for green, purple, 
orange, etc. The risk to railway travellers of employes 
overlooking the red signal of danger, owing to some visual 
defect in the perception of colors, is too serious a matter 
to be lightly passed over. In all parts of the world special 
attention is now being paid to the subject, and the eyes of 
the railway officials are being systematically tested. It is 
difficult to say wherein the defect lies, whether in the optic 
nerve or the retina or the different media through which 
the light travels. If, for instance, the humors of the eye 
themselves have even a slight color, some parts of the light 
will be intercepted before they reach the retina, and the 
image on the retina will therefore be deprived of the colors 
which are intercepted. Suppose, for instance, from any 




Fig. 108. — Stereoscopic Vision'. 



276 • PHYSIOLOGY. 

cause the humors of the eye should have the power of 
intercepting all the blue and violet rays of white light; all 
white objects would appear on the retina as if they had a 
reddish color. 

Stereoscopic Vision. — When we look at an object with 
both eyes the image falls at the same time on the yellow 
spot of each eye, and w T e see but one object. If we press 
on one eye with the finger we see two images, not equally 
distinct, because the image will not fall on the yellow 

spot of that eye. \V r e see only 
one image, indeed, if the light 
falls on corresponding points in 
each eye, whether it be the yel- 
low spot or not. If, however^ 
we look at an object, first with 
one eye and then with the other, 
it will be found that the images produced are different. By 
using a stereoscope, an instrument devised for the purpose 
in which the glasses correspond with the angle of the two 
eyes, the two images are combined and apparent solidity is 
imparted to them. The term stevcoscop' "ic has been applied 
to this kind of vision, from two Greek words meaning " to 
see a solid." 

Vision in the Inferior Animals. — A great variety exists in 
the different classes of animals in the construction of the 
organs of vision. In some of the lower forms of animal 
life the eyes are scarcely anything more than dots capable 
only of distinguishing light from darkness. 

In vertebrate animals — those which have a spinal col- 
umn — there are two eyes, spherical shaped, resting in a 
socket lined with fat as a cushion, just as is the case in 
man. In some fishes, and in some of the lower forms of 
animal life that live both in land and water, the eyelids are 



THE SENSES. 277 

absent and the eyes are covered with a skin. In the cha- 
meleon there is a disc or circle of skin with a central open- 
ing in it, and in some other animals there are not only eye- 
lids, but also a very movable third membrane called the 
nictitating membrane. A familiar illustration of this mem- 
brane is seen in the tortoise. In many birds it can be drawn 
over the whole surface of the eye to protect the organ from 
strong light or from foreign bodies. In the horse there is 
a triangular-shaped cartilage, called the haw, which can be 
drawn closely over the convex surface of the eye for the 
removal of dust or insects. Some animals, as fishes, have 
no tear-apparatus. 

The sclerotic coat is hard in man, but in some animals, 
as birds and lizards, it is composed of cartilage, if not of 
bone. In fishes the eye might suffer by concussion of the 
water against it but for some such arrangement. In some 
animals the choroid or its layer of pigment — which we 
have seen, if present, absorbs the rays of light — is absent, 
so that the eye looks white or metallic. In the cat and the 
lion a portion of the choroid coat is covered with a bluish 
layer with a metallic lustre ; the light is therefore strongly 
reflect?d, so that the eyes seem like balls of fire. The pupil 
is not always round ; it is sometimes elongated vertically, 
as in cats and crocodiles ; sometimes angular, as in some 
toads. In the owl the pupil is much more movable than 
in man. In nocturnal animals — that is, those who seek 
their prey by night — the eyes are usually larger than in 
those which feed during the day ; in the daytime, too, the 
pupil becomei elliptical, appearing almost like a button- 
hole, while at night it is circular, as in man. 

Insects and the Crustacea, which last class includes crabs 
and lobsters, have comjiound eyes, as they are called, or eyes 
made up of an immense number of conical tubes, which go 

24 



278 PHYSIOLOGY. 

off like rays from a common centre, like spokes of a 
wheel placed very closely together, and form a spherical- 
shaped surface on the exterior of the eye. Each ray 
has a sort of cornea or window at" its extremity; in its 
interior a humor like the vitreous humor of the human 
eye, and at its inner end a filament of a nerve, the inside 
of the ray being coated with pigment. All these filaments 
or threads of nerves unite in a single optic nerve. There 
are sometimes from ten to twenty thousand of these tubes 
in a single eye, each one of which is really an eye itself, and 
all of them packed away in a space of a minute fraction 
of an inch. As a matter of interest to the curious, it may 
be stated that the ant has 50 of these eyes, the common 
fly 4000, the silkworm more than 6000, the goat-moth 
more than 11,000, the butterfly more than 17,000, some 
forms of beetle about 25,000. Insects so furnished must 
be provided with eyes for every direction. 

A few other peculiarities of vision in animals generally 
may be briefly stated. Eyes are not always placed, like the 
human eye, symmetrically ; that is, similarly on opposite 
sides of the body. Spiders, for instance, have from half a 
dozen to a dozen eyes placed on a prominent part of the 
back, instead of on the sides of the head. Some animals, 
such as those insects which exist only in dark caverns or 
in deep wells, to which the light never penetrates, are en- 
tirely devoid of organs of sight. Birds are far-sighted, or 
presbyopic (see p. 271), the lens being more flattened than 
in man. Fishes, on the other hand, are near-sighted, or 
myopic. As the water in which they live is a denser me- 
dium than the air, a greater amount of refraction takes 
place ; for this purpose the crystalline lens is more convex 
than in man. 



THE SENSES. 279 

QUESTIONS. 

What useful purpose does vision serve? 

What is the nerve of vision? 

Which pair of cranial nerves is it ? 

In what are the parts necessary to sight contained? 

Of how many coats or coverings is the eye composed? 

What is the course of the fibres of the two optic nerves? 

What parts protect the eye? 

What effect have the tears and sebaceous matter? 

What systems of nerves control these secretions and the movements of 
the eyelids and eyelashes? 

What gland secretes the tears? 

When does the secretion take place? 

What other uses have the tears? 

What finally becomes of the tears? 

What prevents the perspiration from running into the eye? 

What is the socket of the eye? The orbit? 

What is the nature of the protection given the eye by the socket ? 

What is the cornea ? 

Of what use is the fatty matter in the orbit? 

What are the eyelids, and how are they arranged? 

How are they covered and lined ? 

What is the conjunctiva? 

How does it protect the eye ? 

Of what use are the eyelashes? 

How are the edges of the eyelids greased? 

What other useful service does this secretion serve? 

What is the name of the glands which secrete them ? 

What is the anterior chamber of the eye, and what does it contain? 

What is the quantity of the aqueous humor? 

What is the crystalline' lens? 

What is the fluid in the posterior chamber of the eye called? 

How much of the eyeball does it occupy ? 

What is the object of these transparent media ? 

What are the three coats of the eye called ? 

How is the choroid coat arranged to absorb the rays of light? 

What is the nervous coat of the eye called? 

Of what nerve is it an expansion ? 

Through what transparent media must the light pass to reach the 
retina ? 



280 PHYSIOLOGY. 

What is the iris? 

What is the opening in Us centre called ? 

What is the apple of the eye? 

What useful purpose does the pupil serve? 

What system of nerves controls this action? 

What is the shape of the cornea? Its thickness? 

What is the white of the eye? 

What muscles are attached to the sclerotic coat? 

What nerve passes through the back part of this coat? 

What kind of a membrane is the choroid ? 

Which one of the coats of the eye is most largely supplied with blood- 
vessels ? 

What is the purpose of the pigmentary layer of the choroid? 

How are telescopes arranged in a similar way? 

What is an albino? 

What part of the eye gives the color to the eyes of different indi- 
viduals? 

Does the size of the pupil give brilliancy or the reverse to the eye? 

How may the pupil be dilated artificially? 

What kind of a membrane is the retina? 

To what kind of impressions is it sensitive? 

Is the whole of the retina sensitive to light? 

What is the blind spot of the retina? 

In what is the crystalline lens enclosed? 

How thick is the lens? What is its shape? 

What is cataract? 

How is the eyeball moved ? 

How many muscles are connected with the ball? 

What kinds are they ? What action have they? 

Through what number of degrees can the axis of vision be turned 
inward? Outward? Upward and downward? 

What is the cause of luminous sensations? 

What is the correct theory of light? 

Why is it called the undulatory theory? 

What is the rate at which light travels? 

Can sound be explained on similar principles? 

What is the definition of sight on such an explanation? 

What is the estimate of the number of vibrations necessary to pro- 
duce red and violet? 

When does light undergo change in passing through media? 

What is reflection of light? 



THE SENSES. '_2<Sl 

What is refraction of light? 

When light strikes upon the eye, what does it first pass through ? 

What effect has the cornea upon it? 

What effect has the iris upon it ? 

What does the color of the eye depend upon ? 

What are dark eyes dependent upon ? Light eyes? 

What influence has the pupil in controlling the amount of light? 

What nervous action is this dependent upon? 

What is the cause of the refractive power of the lens? 

What is the position of the image on the retina? 

Why do we not see it upside down ? 



What becomes of the two impressions made, one on each eye? 

What becomes of the parallel rays of light in the healthy eye? 

What becomes of these rays in the near-sighted eye? In the far- 
sighted eye? 

What is a myopic eye? 

What is a hypermetropic eye? A presbyopic eye? 

How can the short-sighted eye be corrected ? 

How can the far-sighted eye be corrected ? 

To what is the power of accommodation of the eye due? 

How does this curvature of the lens take place? 

How long does an impression on the retina last? 

What effect has rest on the excitability of the retina? 

By what experiments can we prove that persistent impressions can be 
made on the retina ? 

What is irradiation? How is it explained? 

What is the blind spot of the retina? 

What effect has it on vision? 

W T hat is the yellow spot ? 

What effect has it on vision ? 

What are the seven elementary colors? 

How early in life does this appreciation of color occur? 

What is color-blindness? 

What colors are generally confounded? 

What is the cause of the defect? 

What effect might the humors of the eye have in causing it? 

On what spot of the retina must images fall to ensure perfect vision? 

What is stereoscopic vision? 

What peculiarities of the eyelids are noticed in fishes? 

What third membrane exists in the tortoise? What is its object? 

What cartilaginous arrangement is there in the horse's eye? 
24* 



282 PHYSIOLOGY. 

What peculiarities of the sclerotic coat are found in birds and lizards? 

What changes occur in some animals in the layer of pigment of the 
choroid coat? 

Is the pupil always round, as in man ? 

What peculiarities are noticed in the eyes of nocturnal animals? 

What are compound eyes? 

Describe the arrangement for vision in such eyes. 

How many of these tubules are usually met with ? 

How many has the common fly ? The butterfly ? 

Are eyes always placed opposite, as in man? 

Are there any animals wholly devoid of eyes? 

How does the crystalline lens in birds compare in shape with that of 
man ? 

How does the shape in fishes compare with that of man? 

Why are birds presbyopic and fishes myopic? 



HEARING. 

The Apparatus of Hearing. — The organ of hearing is the 
ear. It consists of three distinct portions — the outer or 
external ear, the middle ear, and the internal ear, in which 
the nerve of hearing is distributed. 

The External Ear (Fig. 109) includes the concha 
("shell") — which is the technical name for the project- 
ing organ on the side of the head familiarly known as the 
ear — and a canal (Fig. 109, a), leading inward, which is 
called the external aud'itory canal or tube. This tube is 
closed at its inner extremity by a membrane called the 
membrane of the tym'panum or drum, having the appear- 
ance in Fig. 109 of a radiated disc. 

The Middle Ear is a cavity filled with air, separated 
from the external ear by the membrane of the tympanum, 
and communicating with the back of the throat by a tube 
(Fig. 109, t>), called the Eustach'ian tube or canal (Fig. 
109, i), named after the anatomist Eustachius, who first 



THE SENSES. 



283 



described it. The membrane of the tympanum is con- 
nected with an opening called the oval window by a chain 
of little bones (Fig. 109, </, e,/). 

The Interned Ear is called the lab'yrinth, because it is 
the most intricate part of the organ of hearing. It is 




Fig. 109.— The Ear. 

(The different parts of the ear are here shown, divested of surrounding hony matter.) 
a, external auditory canal or tuhe; b, Eustachian tube ; /, oval window; o, round 
window; d, e, f, little bones of the ear; i, middle ear; k, vestibule; I, semicir- 
cular canals; m, cochlea. (All the inner parts are here larger than natural.) 

filled with fluid, and consists of three important parts — 
the vestibule, the semicircular canals, and the cochlea 
(Fig. 109, k, i, m). Each consists of a bony and a mem- 
branous portion. The internal ear is the absolutely essen- 
tial portion of the organ of hearing, in which the auditory 



284 



PHYSIOLOGY. 



nerve — the nerve of hearing — is distributed. This nerve 
is one of the seventh pair of eranial nerves. The vesti- 
bule exists in every class of animals in which an apparatus 
for hearing has been detected. The semicircular canals 
are on one side, the cochlea on the other, and the vestibule 
lies between the two. In the wall of the vestibule is an 
opening called the oval window (Fig. 109,/), closed by a 




Fig. 110. — Interior of the Internal Ear. 
A, D, cochlea; B, B, semicircular canals; C, vestibule. 

membrane, and one of the little bones of the ear is in- 
serted into it, as shown at /, Fig. 109. The little bones of 
the ear are called, from their fancied shape, the hammer, 
the anvil, and the stirrup. Their likeness to these articles 
may be seen in Fig 109, d, e,/. The vestibule has seven 
openings communicating with it, and it contains a large 
amount of earthy matter, either hard, like little stones — to 
which the name o'toliths (" ear-stones ") has been given — or 
fine, like dust or powder (" ear-sand "). These doubtless 
have the effect of adding to the force and intensity of the 
sound. Hair-like bodies are noticed on the walls of the 




THE SENSES. 285 

vestibule, in contact with cells connected with the auditory 
nerve. 

"When we examine the labyrinth as a whole we find it 
made up of apartments or chambers and canals which have 
been naturally hollowed out in the temporal bone (Fig. 
111). The osseous or bony labyrinth is nothing more than 
a mould in the hardest part of that bone, containing a 
small quantity of fluid, the 
per'llymph (literally, "the fluid 
around it"). In this mould, 
and surrounded by this fluid, 
is what is called the mem f - 
branous labyrinth, in which 

a Fig. 111.— Thk Cochlea (represcnt- 

organ is the nervous part of ing itg spiral structure ). 

the organ of hearing, bathed 

in another fluid, the en'dolymph (literally, "the fluid 
within it"). The membranous labyrinth consists partly 
of the vestibule communicating with the semicircular canals 
by five distinct openings. Each canal consists of a tube, 
bulging at each end, in which there are cells with long 
hairs. These hairs are the ends of filaments of the audi- 
tory nerve, on which impression must be made in order to 
produce hearing. The other division of the internal ear 
or labyrinth is called the coch'lea ("a snail-shell"), (Figs. 
109, m; 110, a, n). This is a continuous triangular tube, 
turned in a spiral manner, and divided internally in its 
length, by an incomplete partition, into two parts, the lower 
of which extends to the round window, and the other goes 
directly to the vestibule. This spiral arrangement — called 
the seal'ce, or staircases — is well shown in Fig. 111. 

Functions of the External Ear. — The external ear, some- 
times called the auricle, has no other duty connected with 
hearing than to collect the sonorous waves and transmit 



286 PHYSIOLOGY. 

them through the canal to the membrane of the drum of 
the ear. The familiar habit of applying the hand behind 
the ear when we desire to increase our capacity for hearing 
is practised with the view of collecting the vibrations or 
waves of sound, so that they will pass in greater quantity 
and force into the external ear. Some animals lower in 
the scale have very long ears or appendages externally, 
and it has been observed that the loss of such parts is fre- 
quently in them a cause of deafness. In some the auricle 
is trumpet-shaped, and is freely movable, so that sound 
can be collected from all directions. The external auditory 
canal (Fig. 109) is protected from injury from insects and 
foreign bodies by a form of secretion called ear-wax, 
poured out by certain glands called eeru'niinous glands 
(from cerumen, "wax") on its surface, and by the hairs 
that grow along the canal. Even the elevations and de- 
pressions on the outer ear assist in the propagation, of 
sound, and if these be filled up with some soft material, 
so as to make the surface even, the individual cannot hear 
quite as distinctly, or tell in precisely what direction the 
sound is coming. 

Functions of the Middle Ear. — The middle ear — the 
drum or tympanum (Latin for "drum"), as it is generally 
called — is chiefly remarkable for the presence of the small 
bones previously alluded to. These bones are moved by 
very small muscles, and they have the effect, by their mo- 
tions, of rendering the membranes of the tympanum with 
which they are in contact either tight or loose, according 
to the intensity of the vibrations of sound that fall upon 
them. The cavity of the drum of the ear being filled 
with air passing from it to the back of the throat, the 
little bones are allowed free vibration, and the air in the 
middle ear is thus maintained at a uniform temperature. 



THE SENSES. 287 

Another good effect upon the membrane from the presence 

of air here is from the atmospheric pressure being made 
equal on both sides of the membrane of the tympanum or 
drum. It is generally supposed that the tube is closed 
(lu ring: the act of swallowing food or drink, and that it is 
open during repose. 

The chief muscle connected with the membrane of the 
tympanum is called the ten' nor tym'pani (literally, " tight- 
ener of the drum"), which, pulls the membrane inward 
toward the cavity. After it has acted, the membrane re- 
turns to its natural relaxed condition, owing to its own 
elasticity and that of the chain of bones connected with 
it. By means of such movements the membrane is able 
to accommodate itself to the receiving and transmitting 
of sounds of varying pitch — to high sounds when it is 
tense, to low sounds Avhen it is relaxed. When the mem- 
brane of the tympanum vibrates, the vibrations are trans- 
mitted to the internal ear, partly through the air in the 
middle ear and partly along the solid bones — ossicles 
("little bones"), as they are called — the anvil, hammer, 
and stirrup. The power of solid bodies, as of liquids, to 
convey sound is well understood and familiar to every- 
body. These bones weigh only a few grains. 

Functions of the Internal Ear. — In the internal ear sound 
may reach the labyrinth through its bony walls by means 
of the air in the drum of the ear striking upon the round 
window, or through the stirrup-bone which is attached to 
the oval window. Sounds may be distinctly heard that 
have no origin or cause outside the head itself, but which 
may be due to the action of muscles or the passage of blood 
along the bloodvessels in close relation to the nervous por- 
tion of the ear. Hearing is probably effected usually through 
the pulsation or vibration of the little bones, communicated 



288 PHYSIOLOGY. 

to the fluid in the labyrinth, and thence to the minute ter- 
minations of the auditory nerve. 

That hearing may be accomplished it is necessary that 
oscillations in the air, in water, and in solid bodies, which 
give rise to the sensation of sound, should reach the fila- 
ments of the auditory nerve, and that these should be con- 
veyed to the brain for its appreciation. It will be seen, 
therefore, how necessary it is that both the brain and the 
auditory nerve are in a healthy condition. The vibra- 
tions of sound when they fall upon the ear come in contact 
with the vestibule in which is the auditory nerve. The 
whole organ of hearing in the internal ear is so delicate 
and sensitive that the slightest vibration communicated to 
it, and especially to the fluid contained in it, must act upon 
the special nerve of hearing. The vibrations of sound may 
reach the labyrinth through the external ear or through the 
bones of the head. The latter channel may be proved to 
exist by placing a watch between the teeth, when its tick- 
ins: will be distinctly heard. The sound of one's own voice 
is heard in the same way. 

Sound. — In order that sound may be fully appreciated a 
certain amount of fulness is necessary to it. If too feeble, 
no such result will occur ; in other words, hearing will not 
take place. It has been stated by some physiologists, with 
a view of expressing the lowest limit capable of effecting 
sound that will be heard, that it is represented by a pith- 
ball, about -^ of a grain in weight, falling upon a smooth 
piece of glass from a height of Y V of an inch at a distance 
of 3^- inches from the ear. A certain number of vibrations 
is necessary to produce a tone, otherwise sound will not bo 
heard. The lowest limit is said to be about 30 vibrations 
a second, the highest between 30,000 and 35,000. Intensity 
of sound must be distinguished from pitch. Intensity de- 



THE SENSES. 289 

pends on the greater or less degree of fulness of the vibra- 
tions. Pitch depends on the number of vibrations in a 
particular period of time, or, to phrase it differently, on 
the length of time occupied by a single vibration. Quality 
of sound is another element of consideration. It depends 
on the form of the wave of sound that reaches the ear. 
By this appreciation of the quality of sound we are able 
to distinguish the voices of individuals, the sound of 
special musical instruments, etc. 

A sensation of sound lasts, as we have already seen to be 
the case with a sensation of light, after the cause has been 
removed. We are all familiar with such experience. The 
two ears act in harmony, and hear but a single sound, just 
as the two eyes see but a single image, and the brain in the 
two instances appreciates but one object and one sound. The 
eye and the ear have many points in common. The theory 
of sound, as stated under Vision, is based on a similar idea 
to that of the transmission of light ; that is, by waves or 
undulations. There is a physical apparatus — the outer 
portion of the ear — just as there was a physical arrange- 
ment in the eye, before the nerve was acted upon by waves 
of light or of sound. The intensity of sound, as of light, 
is regulated in its action on the ear by a muscular apparatus 
not under the control of the will. 

The Sense of Hearing in Other Animals. — All the higher 
classes of animals possess external ears, which in some of 
them are capable of being turned in various directions to 
catch the sound. In some animals, as the bat, they are out 
of all proportion to their whole size. In some animals the 
outer ear consists of several pieces, instead of one piece, as 
in man. The interior ear does not differ much in different 
animals. Curves of all kinds characterize the semicircular 
canals, some being elliptical, others a portion of a circle, 
25 t 



290 PHYSIOLOGY. 

etc. While in man the cochlea takes two and a half turns, 
it makes nearly four turns in the squirrel and only one and 
a half in the whale. Many of the higher classes of ani- 
mals have the ear lodged in a separate bone — the tympan'ic 
bone — and not in the temporal bone as in man. Birds gen- 
erally are devoid of an exterior ear, but in some of them 
the drum of the ear communicates with cavities in the bones 
of the skull, which act like a sounding-board of a piano to 
increase the resonance, as it is called. In reptiles the organ 
of hearing is imperfect, the external ear and auditory canal 
being sometimes absent, but they possess a drum and its 
membrane, the little bones, and a cochlea. The little ear- 
stones in the internal ear are especially noticeable in fishes, 
some of which possess, as their whole organ of hearing, a 
sacful of such bodies, taking the place of the cochlea, and 
having the nerve of hearing distributed on its walls. There 
is often no other part of the outer ear present except the 
external auditory canal ; the cochlea, too, is straight and 
not coiled as in man. Sometimes there is only one semi- 
circular canal. In the soft forms of animal vegetation 
called the mollusca the vestibule is the only part of the 
internal ear that is present ; in fact, as previously stated, 
this part of the labyrinth is never absent in any animal 
with a denned apparatus for hearing. It contains oscil- 
lating bodies which resemble the otoliths or ear-stones pre- 
viously described. In insects the organ of hearing is said 
to be wholly deficient, but it is possible that it may some- 
times exist where not suspected, as they produce various 
forms of noise by which they call and answer one another. 



THE SENSES. 291 



QUESTIONS 



Of what three parts does the organ of hearing consist? 

To which part is the organ of hearing distributed? 

What two parts compose the external ear? 

What membrane closes the auditory tube at its inner extremity? 

What is the arrangement of the middle ear? 

By what tube does it communicate with the back of the throat? 

What is the labyrinth? 

With what is it filled? 

What three parts make up the labyrinth? 

Of what parts does each consist? 

What is the absolutely necessary portion of the organ of hearing? 

Of which pair of cranial nerves is the auditory nerve a part? 

What is the oval window? 

What are the little bones of the ear called? 

How many openings are there in the vestibule? 

What earthy matter is contained in the vestibule? 

In what bone of the head is the labyrinth placed ? 

What is the difference between the bony and the membranous labyrinth ? 

What is the perilymph ? The endolymph ? 

With what canals does the vestibule communicate? 

"What are the hair-like projections in these canals? 

What is the arrangement of the cochlea? 

What are the two scalse or staircases ? 

What is the auricle of the ear? 

What is its duty ? 

Why do we apply the hand to the ear in order to hear more distinctly ? 

What effect have the long ears of animals ? 

How is the ear protected from injury? 

What are the ceruminous glands? 

What effect have the irregularities of surface of the external ear on 
the sound? 

W T hat is the chief feature of importance in the middle ear? 

How do these little bones move ? 

What is the effect of the presence of air in the middle ear? 

What is the chief muscle called connected with the membrane of the 
tympanum ? 

What is the action of this muscle and its effect on that membrane? 

When the membrane vibrates, how is the sound transmitted' to the 
internal ear? 



292 PHYSIOLOGY. 

How does sound reach the internal ear? 

Do sounds always originate outside the body? What internal sounds 
may be heard ? 

Of what use is the fluid in the labyrinth? 

What organ appreciates or judges of sound? 

What parts must be perfect to ensure perfect hearing? 

Are the vibrations of sound ever communicated through the bony 
walls of the head? 

What conditions of sound itself are necessary to its appreciation? 

What is the lowest limit at which sound can be heard ? 

What is the lowest and highest number of vibrations of sound that 
can be heard by the ear? 

What does intensity of sound depend upon? 

What does pitch depend upon ? 

What does quality of sound depend upon ? 

By which of these can we distinguish voices? 

Does a sensation of sound end at once? 

What facts apply to the eye and ear in common ? 

What peculiarities of the external ear exist in animals? 

What changes in the semicircular canals, cochlea, etc. in animals? 

What special bone have some animals in which the organ of hearing 
is lodged ? 

What peculiarities are found in birds? In reptiles? In fishes? In 
the mollusca? In insects? 



VOICE. 



The Organ of Voice. — The voice is produced by vibra- 
tion of the vocal cords in the larynx while the air is pass- 
ing through it. Speech differs from voice, being the use 
of sounds to express ideas. Speech is therefore an appli- 
cation of the voice. It 
is this power to convey 
thoughts by the voice that 
creates a wide distinction 
between man and other ani- 
mals. The arrangement of 
organs for the production 
of the voice may be brief- 
ly said to consist of the 
larynx, the windpipe, the 
lungs, the mouth and nose, 
and the muscles concerned 
in breathing, for one and 
all are directly or indi- 
rectly interested in it. 

The Larynx. — The lar- 
ynx (Fig. 112) is sit- 
uated in the front part 

Of the neck, being more trachea or windpipe; 4, ligament. 

prominent in the male, in whom it forms a very con- 
spicuous object, commonly known as " Adam's apple." 
The mucous lining membrane of the mouth and throat 

25 * 293 




Fig. 112. — The Larynx (front view). 
1, thyroid cartilage; 2. cricoid cartilage; 3, 



294 



PHYSIOLOGY. 



is continued downward into the larynx, and thence into 
the windpipe, which is a continuation of the larynx. The 
larynx is a tube made up of four cartilages, united together 
by ligaments, and having muscles attached to them. These 

bodies are movable 
upon one another, the 
object of which mo- 
bility will be presently 
explained. 

The Vocal Cords. — 
The interior of the lar- 
ynx is the part most 
directly interested in 
the production of voice. 
When we examine this 
portion of the organ 
we notice two clefts, or 
triangular spaces (Fig. 
113). The upper one 
is bounded laterally by 
two folds of mucous 
membrane, called the 
upper, or superior or 
false vocal cords ; the 
lower one by two folds, 
called the lower, or in- 
ferior or true vocal 
cords. Between these 
two spaces or cavities 




Fig. 113. — Interior of the Larynx. 



upper or superior vocal cords ; - 2, lower or in- 
ferior vocal cords; 3, epiglottis ; 4, thyroid car- 
tilage; 5, vertical section of the glottis ; 6, ary- 
tenoid cartilage; 7, section of cricoid cartilage ; 
8, muscle between cricoid and arytenoid carti- 
lages; 9, trachea or winupipe. 



are 



the 



veil 



'tricles of 



the larynx, whose sides are mainly formed of muscles. The 
vocal cords are perfectly free to move, and are not inter- 
fered with in their action by any other structures. The 



VOICK. 



295 




vocal cords are only separated from one another about a 
third of an inch. The general plan of 
these spaces and cords will be readily 
understood by the accompanying dia- 
gram (Fig. 114). 

Muscles of the Larynx. — The whole 
larynx may be moved at once, or only 
a part at a time. The muscles which 
are more directly concerned in the pro- 
duction of voice are those which are 
generally called the intrin'sic muscles 
of the larynx, which are so placed as , 
to be capable of exerting some influence cai view). 
by their contraction or relaxation on i, folds between arytenoid 
this delicate vocal organ. The effect 
of their action is either to render the 
vocal cords or ligaments tense, or to 
separate the cartilages from one another, 
so as to open the glottis (Fig. 113, 5), as the space of about 
a fifth ,of an inch in extent between the inferior vocal cords 
has been called, or to bring them together so as to close the 
glottis, or to relax the inferior or true vocal cords by draw- 
ing back the thyroid cartilage. Some of the muscles at- 
tached to the upper part of the larynx change the position 
of the epiglottis (Fig. 113, 3). 

All these movements of parts are necessary to produce 
the changes of sound which are characteristic of the voice. 
The degree of tension of the vocal cords is also regulated 
by the action of muscles. As in all the special senses, the 
production of voice requires that the physical apparatus 
shall be perfect, and that the nervous supply to the organs 
shall be unimpaired. Nerves are distributed to the in- 
trinsic muscles, and through them the muscular action in 



Fig. 114. — Interior of 



and epiglottis; 2, supe- 
rior or false vocal cords; 
3, inferior or true vocal 
cords ; V, V, ventricles of 
the larynx; T, trachea 
or windpipe. 



296 PHYSIOLOGY. 

the production of voice is controlled and regulated. It 
can be readily seen that if these nerves should be injured 
or divided the action of the muscles would be checked, so 
that the conditions necessary to the production of voice 
could not exist. 

Production of Voice. — In order to produce the voice it 
is necessary that the air should pass from the lungs through 
the windpipe into the larynx, cause a vibration of the vocal 
cords, and thence pass outward through the mouth and cav- 
ities of the nose. This is of course produced under the 
influence of the will, for otherwise voice would be pro- 
duced at every breathing movement. The inferior vocal 
cords (Fig. 113, 2) are the parts of the larynx directly con- 
cerned in the production of the voice. It has been said 
that every other part of the larynx can be destroyed, and 
the voice may still be produced if these cords are left un- 
touched. The appearance of the vocal cords at the moment 
of emission of the voice is represented in Fig. 116, a. 

The passage of air through the glottis may be illustrated 
as follows : Take two pieces of bladder or India-rubber 
and stretch them over the open end of a 
tube, as represented in Fig. 115, so that 
each shall cover rather less than the open- 
ing, a space being left between them. If 
air be forced upward through such a tube 
by bellows a sound will result if the open- 
ing between the membranes be not too wide. 
heory rp| ie goun( | can j^ ma( j e t imitate the voice 

of the Glottis. 

of an animal. If the membranes be made 
tighter or looser the sound will vary in character. 

Some writers on the larynx have described it as a wind 
instrument of the flute kind, or as being like a horn, the 
vibrations in those musical instruments being caused by a 




voice. 297 

column of air passing through them ; others have spoken 
of it as a stringed instrument, on account of the part taken 
by the vocal cords in the production of sound. Most 
writers, however, think it resembles more closely a reed 
instrument, like a clarionet. No matter what we may 
compare it to, the process of production of the voice is 
not at all simple. It includes a great variety of acts — the 
sending of air into the larynx, the contraction,of the mus- 
cles of the larynx producing tension of the cords, their 
vibration, and the passage of air outward through the 
mouth. 

The larynx is more developed in the male than in the 
female, and hence his voice is much stronger. Even when 
this organ is fully developed its action may be impaired 
by disease, although the disease may not be seated in the 
organ of voice. General debility may weaken the "indi- 
vidual so much, as after severe sickness, that the muscles 
of the voice have not the power given to them to send the 
air through the larynx with such force as to cause the 
necessary amount of vibration of the cords. 

Intensity and Pitch of Voice. — The intensity of the voice 
depends mainly on the force with which the air is driven 
through the larynx • in other words, on the pressure of the 
air. The number of vibrations of the cord in a given 
time produces the pitch of the voice. This is regulated by 
the degree of tension of the cords and the width of the 
space between them. AVhen we wish to produce tones of 
high pitch we bring the edges of the cords more closely 
together, so that they become more tense (Fig. 116, c). 
When we wish to produce a low pitch the edges of the 
cords are separated (Fig. 116, b). By means of an instru- 
ment called a laryn' goscope (from two Greek words mean- 
ing " inspection of the larynx ") which enables an observer 



298 PHYSIOLOGY. 

to see, by means of a mirror, the interior of the larynx 
and the movements of its various parts during the pro- 
duction of sound, it has been noticed that before sound 
is produced the glottis is partly or completely closed by 






Fig. 116. — The Glottis and Vocal Cords in Singing, as seen with the 

Laryngoscope. 
A, opening of the glottis in the chest-voice and in ordinary inspiration; B, chest 
voice, for low notes especially ; 0, opening of the glottis in the falsetto voice or in 
High notes. The interval between the vibrating vocal cords is the glottis. 

the bases of the arytenoid cartilages coming together, and 
the cords made tense, after which they are separated by the 
air passing between them and thrown into violent vibra- 
tion. The full voice is not produced by the vocal cords 
alone, being intensified by the movement of the air in the 
cavity above it. 

The .number of vibrations of the cords on which the 
pitch depends is of course influenced by the length of 
the cords, their size, and the amount of tension. The 
longer the cords the lower the pitch ; the tighter the cords 
the higher the pitch. 

Quality of Voice. — It is difficult to explain the difference 
in quality of voice between individuals. Every person has 
his own quality, which belongs to him peculiarly and dis- 
tinguishes him from every one else. The voice of the 
female is due to the fact that the larynx is more carti- 
laginous than in the male. The thickness of the walls, 
the size of the cavities, the form and length of the tube, 
probably affect the quality of voice. The presence or ab- 



voice. 299 

sence of the teeth and the shape of the tongue also have 
an influence. The change of voice in boys of about twelve 
to fourteen years of age is due to the fact that the ligaments 
and the opening of the larynx then become enlarged. In 
addition to the voice, as naturally affected, other sounds are 
capable of being produced from the vocal tube. Whisper- 
ing is nothing more than articulation of the air that is 
breathed out of the vocal tube ; whistling is caused by 
dividing the air as it passes through the lips. 

The Singing and the Speaking Voice. — The human voice 
extends over a range of about three octaves in singing. The 
voice in singing differs from the ordinary voice in speaking 
by being made up of distinct musical tones, following in 
regular order in sequences, as they are called. The range 
of the singing voice is illustrated in Fig. 117, but this only 
shows the ordinary average. The quality and compass of 
voice vary greatly in different persons and in the two sexes. 
The deepest male voice is the bass, the highest the tenor, 




Fig. 117.-^Range op the Singing Voice. (The figures denote the different 

octaves.) 

and the baritone occupies a place between these two. The 
lowest female voice is the contralto or alto, the highest 
the soprano, and the intermediate voice the mezzo-soprano. 
When bass singers are capable of high notes the quality or 
tone is different from that of tenor or -soprano singers. -A 



300 t PHYSIOLOGY. 

flute and a clarionet may both strike the same note, but the 
tone or quality will greatly differ. The range of the different 
forms of singing voice is well illustrated in the diagram 
(Fig. 117). The singing voice is generally from the larynx 
— chest-voice it is then called — but sometimes also from 
the throat or pharynx. Cases are on record in which a 
range of three and a half octaves was reached. The laryn- 
geal voice is usually an octave higher in woman than in 
man. The range of the human voice is generally consid- 
ered to be three octaves, say from low fa or faj (generally 
known as F l on the scale of the piano), representing 174 
vibrations a second, to high sol or sol 4 , representing 1566 
vibrations. The inferior or true vocal cords in men are 
longer than those of women in the ratio of 3 to 2, the con- 
sequence of which is that the male voice is stronger and 
lower in pitch. Exceptional voices have been known in 
which there was wonderful range, as an Italian singer, 
named Lucrezia Ajugari, to whom Mozart listened more 
than a century ago, whose lowest note indicated 391 vibra- 
tions, the highest 4176. The notes produced in singing 
are either chest notes, falsetto notes, or head notes. The 
deepest notes are those from the chest, the highest from 
the head. 

Sounds are sometimes produced apparently from parts 
deep down in the chest by the ventriloquist, as he has been 
called. The word ventriloquism is derived from two words 
meaning "speaking from the stomach," and it would appear 
possible that this might be true, judging from the depth 
and distance of the sounds emitted. It is, however, nothing 
more than a deception dependent upon the power of the in- 
dividual to manage his voice as it proceeds from the larynx 
and mouth, and to mislead his audience as to the direction 
and quality of the sounds he utters. The different actions 



VOICE. 301 

and appearances of the larynx in the production of va- 
rious voices is well shown in Fig. 116. 

The strength of the voice depends upon the muscular 
movements regulating the action of the vocal cords, and 
not so much on the current of air passing through the 
larynx. These muscles are only about three quarters of 
an inch Ions:, and all the different musical notes and tones 
are produced by the most delicate adjustment and varia- 
tion of them. It is supposed that they can be accurately 
varied to a movement of l-1200th to the 1-1 2000th of an 
inch. 

The Formation of Language. — Speech, as already stated, 
is a series of articulate sounds to convey ideas, and is under 
the control of the will. Of course if a person has not the 
ideas to express, as is the case with the idiot, the presence 
of a perfect vocal apparatus will be of no use to him, as he 
is not capable of framing his ideas in words. Speech may 
be considered an evidence of the possession of intellect, and 
the quality of the intellect is often evidenced by the quality 
of the speech indulged in by its possessor. A parrot may 
speak distinctly, but its brain does not appreciate the mean- 
ing of what it says. Originally, before language was formed, 
words were probably derived from familiar sounds, such as 
the cries of wild beasts, the notes of birds, etc. The very 
names given to some of these sounds, as hissing, humming, 
snoring, grunting, whistling, wind, etc., are intended as 
nearly as possible to convey a notion of the sound itself. 
Words expressing such sounds in one language can be 
traced through a dozen other languages. The word 
" cuckoo," which is but the vocal expression of the cry of 
the bird, is said to be very much the same word in Greek, 
Latin, German, Arabic, Dutch, French, Persian, and a 
number of other languages. The clucking of the hen, 

26 



302 PHYSIOLOGY. 

crowing, neighing, and bleating of various animals are 
reproduced in different languages. A " crash " is but an 
imitated sound, and so is a " thud," or dull, heavy sound 
or blow. 

Vowels and Consonants. — The sounds that make up words 
are reduced to elementary ones, which we call letters, which 
placed together form syllables, and these again make up 
words. An alphabet is a collection of all the letters used 
in a language. The letters, or articulate sounds, are either 
vow r els or consonants; the vowels being musical tones 
formed in the larynx, and passing out uninterrupted by 
the tongue or lips, although these occupy different positions 
in the production of the sound of each vowel. The strength 
of the sound is increased by the resonance of the air in the 
cavities of the mouth and pharynx. The name Aa (Danish 
for " river ") has been given to several rivers, probably be- 
cause as pronounced it represents the most easy and un- 
impeded flow of sound. Consonants are sounds formed 
in some part of the air-passages above the larynx, as the 
mouth, and increased in force by the action of the larynx. 
Some of them seem to come from the throat and base of 
the tongue, and are called gut'tural sounds, such as eh and 
j ; those from the tongue and front part of the roof of the 
mouth are called ling'uals, as s and sch ; those from the 
lips la'bials, as b, p. Some consonant sounds have a nasal 
quality imparted to them from a portion of the air passing 
into the passages of the nose — m, n, ng, for example. Some 
letters are called explosives, because they are uttered sud- 
denly and cannot be sustained, as b, d, g, p. As these 
sounds do not often occur in Italian, that language is 
considered a much more agreeable one for the singer than 
either German or English. 

The Voice and the Hearing. — We have already seen that 



• voice. 303 

taste ami smell depend upon each other for their perfec- 
tion, and it is equally true that sight and touch are neces- 
sary to each other's full exercise. So, too, with the voice 
as connected with hearing. The vocal organs of a child 
may be absolutely perfect, but if hearing is wholly extinct 

from birth he cannot use articulate language, which in- 
to o " 

eludes the proper use of words to express ideas. He can- 
not, in other words, repeat sounds that he has never heard, 
and is therefore dumb as well as deaf. A person who has 
not a " musical ear " — that is, cannot appreciate harmony 
or melody in music — can never be an accurate singer, for 
he cannot reproduce sounds that he does not understand. 
Vocal Apparatus of Animals. — The sounds emitted by 
animals are sometimes produced by their organs of respi- 
ration, but often through other means. Birds are endowed 
with very active respiratory organs, as we have already 
seen, and their continuous song is therefore much more 
easy than would be possible in almost all other animals. 
Some insects produce their familiar noises by the rapid 
motion or vibration of their wings — the mosquito, for in- 
stance. The friction against one another of the different 
hard parts of the cricket produces the peculiar shrill chirp 
which is so characteristic of that little animal. The grass- 
hopper's shriek is produced by the animal rubbing its legs 
against its wings. It is said that in some parts of South 
America there exists a locust which has a kind of drum 
under its wings, the sound of which can be heard a mile or 
more : if a man of ordinary size had a voice in proportion 
it would be heard from one end of the Avorld to the other. 
Those insects which fly most rapidly are the noisiest. The 
hiss of the tortoise and other reptiles and the croak of the 
frog are produced by a vibration where the windpipe opens 
into the pharynx. 



304 PHYSIO LOG V. 

In birds the important part of the vocal organs is at the 
lower part of the trachea or windpipe before it divides into 
the bronchial tubes. A sort of bony drum is present at 
this location in some birds, which is less simple in construc- 
tion in birds that do not sing than in those which do. There 
is a small membrane of a crescentic or half-moon shape at- 
tached to a cross-bone, and when this membrane vibrates it 
produces the trill so familiar in the best singing-birds. 



QUESTIONS. 

How is the voice produced ? 

What is the difference between voice and speech? 

What are the organs concerned in voice ? 

What is the prominence in the neck called in man? 

What kind of a lining membrane has the larynx? 

What is the larynx ? 

What is the appearance of the interior of the larynx? 

What are the true vocal cords? 

What are the ventricles of the larynx? 

How far apart are the inferior vocal cords? 

By what is the larynx moved? 

What effect have the intrinsic muscles on the vocal cords? 

What is the glottis? 

What effect have the nerves in the larynx on the voice? 

What action is necessary to the production of the voice? 

Is voice voluntary ? 

What parts of the larynx are absolutely essential to the production of 
voice ? 

What kind of a musical instrument is the larynx? 

What different actions does the production of voice include? 

Is the larynx more developed in the male or the female? 

What does intensity of the voice depend upon ? 

What does the pitch depend upon? 

What different action takes place in the cords when we wish to pro- 
duce high or low notes? 

What is the laryngoscope? 

How is the full voice produced ? 

On what does the number of vibrations of the cords depend? 



VOICE. 305 

What effect has a long cord on the pitch? A tight cord? 

To what is the difference in voice of the sexes due? 

What conditions arlect the quality of the voice? 

What change takes place in the larynx in boys? 

What is whispering ? What is whistling ? 

What is the deepest male voice called ? The highest? 

What intermediate voice is there in the male? 

What is the highest female voice? The lowest? 

What intermediate voice is there in the female? 

What is the range of the singing voice? 

How much higher is the laryngeal voice in woman than in man ? 

What is usually the lowest and the highest number of vibrations in 
the human voice ? 

What is the relative strength, etc. of the vocal cords in man and woman ? 

How are the notes produced in singing divided ? 

Which are the deepest notes? 

What is ventriloquism? 

What is speech ? 

What does strength of the voice depend upon ? 

What effect follows the minute vibrations of these muscles? 

What defect of speech has the idiot? 

How was language first formed ? 

On what principle are words like "hissing," "snoring," "grunting," 
"cuckoo," etc. derived? 

What are elementary sounds called that make up words? 

What is an alphabet? 

What two divisions are there of letters? 

What are vowels? How are they formed? How are they increased 
in strength ? 

What are consonants? How are they formed? 

Into what divisions are consonants divided? 

How are nasal sounds produced? 

What are the explosive consonants? 

How are the voice and hearing related to one another? 

Why is a deaf person usually dumb also? 

How are the sounds or voices of animals produced? 

How do insects produce their pecidiar sounds? 

How is the noise of the cricket produced ? 

How is the sound of the grasshopper caused ? 

How is the croaking of the frog produced ? 

What is the anatomical arrangement in the windpipe of birds for singing ? 
26* U 



INDEX. 



\ 



Abdomen, 87. 
Absorption, 49, 120. 

intestinal, 49, 120, 121. 

of chyle, 121, 123. 
Accommodation of eye, 291. 
Adam's apple, 293. 
Ages, 13. 

Air, atmospheric, 138. 
Air-cells, 133, 137. 
Albumen, 18, 56. 

vegetable, 18. 
Albuminous substances, 56. 
Aliments, 50. 
Anatomy, 10. 

comparative, 10. 
Animal food, 58. 
Animal heat, 179. 
Animals, nutrition of, 15. 
Animals and vegetables, chemistry 
of, 16. 

differences between, 14. 
Antagonistic muscles, 40. 
Anterior chamber of eye, 26. 
Anvil of ear, 284. 
Aorta, 158. 
Aponeurosis, 39. 
Appendix of ccecum, 103. 
Appetite, 72. 
Apple of the eye, 264. 
Aqueous humor, 263. 
Arbor vitae, 199. 
Arterial blood, 129. 
Arteries, 23, 151, 158. 
Articulations, 35. 



Atmosphere, 138. 
Auditory canal, 282. 
Auricle of ear, 285. 
of heart, 150. 

Ball of the eye, 256. 
Beat of heart, 154. 
Bile, 104, 106. 
Biliousness, 99. 
Birds, circulation in, 165. 

digestive apparatus of, 93. 

hearing in, 290. 

nervous system of, 225. 

respiration of, 142. 

smell in, 245. 

taste in, 239. 

vision in, 277. 

vocal organs of, 303. 
Birds as food, 5S. 
Blind spot of retina, 274. 
Blood, 167. 

coagulation of, 172. 

crystals of, 172. 

matters secreted from, 184. 

quantity of, 158. 
Blood-corpuscles, 138, 168. 
Blood-globules, 138, 168. 
Bloodvessels, 23. 
Boiling, 65. 
Bolting of food, 84. 
Bones, 27. 

division of, 28. 

structure of, 28. 
Brain, 192, 193, 197. 

307 



308 



INDEX. 



Brain, convolutions of, 197. 

hemispheres of, 198. 

size and weight of, 194. 
Branchiae of fishes, 143. 
Brandy, 69. 
Bread, 63. 
Breathing, act of, 134. 

mechanical actions of, 139. 
Broiling, 65. 
Bronchial tubes, 132. 

Canine teeth, 76. 
Capillaries, 162. 
Cardiac extremity, 88. 
Carnivorous animals, 79, 87. 
Cartilage, 2S, 35. 
Cartilages of larynx, 294. 
Casein, 18, 56. 
Cauda equina, 207. 
Cells, 19. 
Cerebellum, 193, 199. 

functions of, 215. 
Cerebro-spinal axis, 192. 

fluid, 193. 

system, 190, 192. 
Cerebrum, 193. 

functions of, 216. 
Ceruminous glands, 286. 
Cheese as food, 61. 
Chemistry, 11. 

an aid to physiology, 11. 

of animals and vegetables, 1( 
Chest, 130. 

contents of, 130. 

sounds of, 136. 
Choroid coat, 264, 265. 
Chyle, 50, 107. 

absorption of, 121. 
Chyliferous vessels, 107. 
Chylifieation, 107. 
Chyme, 96. 
Cilia, 133. 
Circulation of the blood, 148. 

in animals, 164. 



Circulation of the blood, greater, 152. 

lesser, 152. 

objects of, 148. 

pulmonic, 152. 

systemic, 152. 

velocity of, 162. 
Clot, 173. 

Coagulation of blood, 172. 
Cochlea, 283, 285. 
Coecuin, 102. 

Cold-blooded animals, 179. 
Colon, 102. 
Color-blindness, 275. 
Colors, perception of, 275. 
Columus of cord, 206. 
Concha, 282. 
Condiments, 51. 
Conjunctiva, 262. 
Consonants, 302. 
Contractility, 39. 
Convolutions of brain, 197. 
Cooking, modes of, 64. 
Cords, vocal, 294. 
Corium, 24S. 
Cornea, 262, 265. 
Corpuscles of blood, 138, 168. 

of touch, 250. 

white, 171. 
Coughing, 139. 
Crustacea, circulation in, 167. 

vision in, 277. 
Crystalline lens, 263, 266. 
Cutis, 248. 

Death, 13. 

Deglutition, 82. 

Dentine, 76. 

Derma, 248. 

Dextrine, 81. 

Diaphragm, 87, 130. 

Diastole of heart, 154. 

Diet, conditions necessary for, 71. 

Digestibility of food, 98. 

Digestion, 49. 



INDEX. 



309 



Digestion, aids to, 99. 

apparatus for, 74. 

buccal, 84. 

duration of, 98, 100. 

in animals, 91. 

in intestines, 101. 

in stomach, 86. 

in the vegetable, 49. 

oral, 84. 

processes of, 84. 
Divisions of the body, 21. 
Dreaming, 219. 
Drinks, 65. 
Drum of ear, 286. 
Duodenum, 101. 

Ear, 282. 

bones of, 284, 287. 

external, 282, 285. 

internal, 283, 287. 

middle, 282, 286. 
Ear-sand, 284. 
Ear-stones, 284, 287. 
Ear-wax, 286. 
Eggs, 62. 
Emulsion, 54. 
Endocardium, 149. 
Endolymph, 285. 
Epidermis, 248. 
Epiglottis, 84. 
Eustachian tube, 282. 
Exercise, effect of, 42. 
Expiration, 134. 
Extensor muscles, 40. 
Eye, 258. 

accommodation of, 271. 

coats of, 264. 

color of, 265, 269. 

far-sighted, 272. 

hypermetropic, 272. 

in animals, 276. 

myopic, 271. 

presbyopic, 272. 

protection of, 256. 



Eye, short-sighted, 271. 

transparent parts of, 262. 
Eyeball, 256. 

motions of, 266. 
Eyelashes, 259. 
Eyelids, 258. 

Facial angle, 196. 

Fat-cells, 19. 

Fats, 54. 

Ferments, action of, 63. 

Fibrils, 36. 

Fibrin, 18, 56. 

Fifth pair of nerves, 203. 

Fish as food, 60. 

Fishes, circulation in, 165. 

digestive apparatus of, 93 

hearing in, 290. 

respiration in, 143. 

smell in, 245. 

vision in, 277-. 
Flesh, 36, 58. 
Flexor muscles, 40. 
Flour, composition of, 51. 
Fluids at meals, 100. 

thin, digestion of, 98. 
Food, animal, 58. 

classification of, 53. 

digestibility of, 98. 

ingredients of, 52. 

of man, 50. 

quantity of, 69. 

vegetable, 58, 62. 
Frugivorous animals, 79. 
Fruits, 63. 
Frying, 65. 

Gall-bladder, 106. 
Ganglionic system, 190. 
Ganglions of brain, 198. 

of nerves, 201. 

sympathetic, 210. 
Gases in body, 18. 
Gastric juice, 88. 



310 



INDEX. 



Gelatin, 58. 
Gills, 143. 
Gin, 69. 
Glands, 185. 

ceruininous, 286. 

lachrymal, 257. 

lymphatic, 123. 

Meibomian, 262. 

salivary, 76, 80. 
Globe of the eye, 256. 
Globulin, 18. 

Glosso-pharyngeal nerve, 237. 
Glottis, 295. 

in singing, 298. 
Gluten, 56. 

Graminivorous animals, 79, 87. 
Gum, 56. 

Hair, 252. 

color of, 252. 
Hair-follicle, 252. 
Hammer of ear, 284. 
Hand, 254. 
Hearing, apparatus of, 282. 

in animals, 289. 

nerve of, 284. 

sense of, 282. 
Heart, 148. 

aortic, 152. 

arterial, 152. 

beat of, 154. 

cavities of, 150. 

left, 150. 

lymphatic, 126. 

movements of, 154. 

pulmonary, 152. 

right, 150. 

sounds of, 155. 

systemic, 152. 

valves of, 152. 

venous, 152. 

vitality of, 155. 
Hemispheres of brain, 198. 

in animals, 222. 



Herbivorous animals, 87. 
Hunger, 72. 

in the vegetable, 73. 
Hygiene defined, 14. 
Hypermetropic eye, 272. 
Hypoglossal nerve, 237. 

Ichthyophagous tribes, 60. 

Ileum, 101. 

Imbibition, 123. 

Infusion, 163. 

Inorganic bodies, 9, 12. 

Insalivation, 76. 

Insects, circulation in, 166. 

digestive apparatus of, 93. 

hearing in, 290. 

nervous system of, 224. 

noise of, 303. 

respiration in, 144. 

smell in, 245. 

taste in, 238. 

touch in, 253. 

vision in, 277. 
Inspiration, 134. 
Intestinal juices, 104. 
Intestines, digestion in, 101, 107. 
Iris, 264, 265. 
Irradiation, 273. 
Ivory of teeth, 76. 

Jejunum, 101. 
Joints, 34. 

Koumyss, 61. 

Labyrinth, 283. 

bony, 285. 

functions of, 287. 

membranous, 285. 
Lachrymal gland, 257. 
Lacteals, 107. 
Lake water, 67. 
Language, formation of, 301. 
Laryngoscope, 297. 



INDEX. 



311 



Larynx, 132, 293. 

cartilage^pf, 294. 

muscles of, 295. 

ventricles of, 294. 
Laughter, 139. 
Leaping, 42. 
Legiunin, 18. 

Lens, crystalline, 263, 266. 
Ligaments, 35. 
Light, 267. 

reflection of, 267. 

refraction of, 267. 
Limbs, 32. 
Lingual nerve, 237. 
Liquor sanguinis, 172. 
Liver, 86, 106. 
Lungs, 130, 131. 
Lymph, 121. 
Lymphatic glands, 123. 

heart, 126. 
Lymphatics, 23, 120, 124. 

valves in, 125. 

Malt liquors, 68. 
Mammalia, circulation in, 164. 
Marrow of bone, 29. 

spinal, 192. 
Mastication, 76. 
Meat, 36. 
Medulla oblongata, 193. 

functions of, 214. 
Meibomian glands, 262. 
Membrane of tympanum, 282. 
Milk, composition of, 51. 

as food, 60. 
Molar teeth, 76. 
Mollusca, hearing in, 290. 

nervous system of, 223. 
Mouth in digestion, 75. 
Mouth-watering, 80. 
Movements of the body, 41. 

nervous centre controlling, 217. 
Muscles, 22, 36. 

fibres of, 36. 



Muscles, names of, 43. 

of expression, 43. 

striated, 38. 

striped, 38. 
Myopic eye, 272. 

Nails, 253. 
Nerve-cells, 191. 
Nerve-fibres, 191. 
Nerves, 23, 190, 200. 

cranial, 203. 

functions of, 211. 

injuries to, 206. 

of respiration, 208. 

spinal, 205. 
Nerve-sheath, 201. 
Nervous matter, 191. 
Nervous system, 188. 

divisions of, 190. 

functions of, 210. 

of animals, 221. 
Nitrogenized food, 53. 
Non-nitrogenized food, 53. 
Nose, 240. 
Nucleolus, 19. 
Nucleus, 19. 
Nutrition in cells, 19. 

Odors, 242. 

(Esophagus, 82. 

Oils, 54. 

Olfactory nerve, 203, 241. 

Omnivorous animals, 79. 

Optic nerve, 203, 256. 

Orbits, 258. 

Organized bodies, 9, 12. 

Ossicles of ear, 284, 287, 

Otoliths, 284. 

Oval window, 283, 284. 

Pancreatic juice, 104. 
Pancreatin, 85. 
Panting, 139. 



312 



INDEX. 



Papillae of skin, 247, 249. 

of tongue, 234. 

of touch, 247, 249. 
Parotid gland, 82. 
Pelvis, 31. 
Pepsin, 63, 85, 89. 
Peptone, 18. 
Pericardium, 149. 
Perilymph, 285. 
Periosteum, 34. 
Peritoneum, 102. 
Permanent teeth, 76. 
Pharynx, 82. 
Phrenology, 218. 
Physics an aid to physiology, 11. 
Physiology, aids to, 11. 

comparative, 9. 

human, 9. 

vegetable, 9. 
Pigment-cells, 21. 
Pleura, 132. 
Pons Varolii, 194. 
Portal vein, 98. 
Prehension of food, 84. 
Presbyopic eye, 272. 
Ptyalin, 85. 
Pulmonary arteries, 138. 

veins, 138. 
Pulse, 156. 
Pulse-writing, 160. 
Pupil, 264. 
Pylorus, 88, 106. 

Rain water as drink, 66. 
Rectum, 102. 
Reflection of light, 268. 
Reflex action of spinal cord, 213. 
Refraction of light, 268. 
Reptiles, circulation in, 165. 

digestive apparatus of, 93. 

hearing in, 290. 

respiration in, 144. 

smell in, 245. 

taste in, 238. 



Respiration, 128. 

changes in, 128. " 

full, 136. 

gentle, 135. 

in animals, 142. 

in vegetables, 144. 

nerves of, 135, 208. 

obstacles to, 140. 
Respirations, number of, 135. 
Retina, 264, 266. 

image on, 270. 

impression on, 272. 
Ribs, 130. 

River water as drink, 67. 
Rum, 69. 
Rumination, 92. 
Running, 41. 

Saliva, 76. 

Salivary glands, 76, 80. 

structure of, 82. 
Scent of animals, 245. 
Schneiderian membrane, 240. 
Sclerotic coat, 264, 265. 
Sebaceous glands, 251, 262. 
Secretion, 184. 
Semicircular canals, 283. 
Sensation, 216, 231. 
Senses, 231. 

corporeal, 232. 

intellectual, 232. 
Serum, 17, 173. 
Short-sight, 271. 
Sight, 255. See Vision. 
Skeleton, 21. 
Skin, 248. 

color of, 253. 

papillae of, 247, 249. 

true, 248. 
Sleep, physiology of, 218. 
Smell, how effected, 243. 

in animals, 244. 

nerve of, 241. 

organ of, 240. 



INDEX. 



313 



Smell, uses of, 243. 
Smelling, 140, 243. 
Sneezing, 140. 
Sobbing, 139. 
Sockets, 258. 
Sound, 288. 

intensity of, 288. 

pitch of, 288. 

quality of 28S. 
Sounds of chest, 136. 

of heart, 155. 
Speech, 293. 
Spinal canal, 30. 

cord, 192. 

marrow, 192. 

reflex actions of, 212. 

termination of, 207. 
Spine, 22, 29. 
Spirits, 69. 

Splenic extremity, 88. 
Sprains, 35. 
Spring water, 67. 
Starch, 55. 

Stereoscopic vision, 276. 
Stewing, 65. 
Stigmata, 144. 
Stirrup of ear, 284. 
Stomach, 86. 

anatomy of, 87. 

digestion in, 86, 95. 

of animals, 91. 
Sublingual gland, 82. 
Submaxillary gland, 82. 
Sudoriferous glands, 250. 
Sugar, 55. 
Sutures, 28. 
Sweat, 250. 
Sweat-glands, 250. 
Swimming, 42. 
Sympathetic nerve, 190, 208. 

system, 190, 208. 
Systole of heart, 154. 

Taste, 232, 235. 

27 



Taste, in animals, 238. 

national differences of, 238. 

organ of, 232. 

sense of, 232. 
Tears, 257. 
Teeth, 76. 

bicuspid, 76. 

canine, 76. 

incisor, 76. 

milk, 76. 

molar, 76. 

permanent, 76. 

temporary, 76. 

wisdom. 77. 
Temperature of animals, 179. 
Temporary teeth, 76. 
Tendo Achilles, 39. 
Tendons, 38. 
Tensor tympani, 287. 
Thirst, 74. 
Thoracic cansil, 122. 

duct, 122. 
Thorax. See Chest. 
Tongue, 80, 233. 

muscles of, 237. 

nerves of, 237. 

papillae of, 234. 
Touch, 247. 

in animals, 253. 

organ of, 247. 

papillae of, 247. 

sensation of, 254. 
Touch-bodies, 247, 250. 
Touch-corpuscles, 247, 250. 
Trachea, 132. 
Transfusion, 163. 
Trichina spiralis, 58. 
Tympanic bone, 290. 
Tympanum, 286. 

membrane of, 282. 

scalae of, 285. 

Unditlatory theory of light, 267. 
of sound, 267, 288. 



314 



INDEX. 



Valves of heart, 152. 

mitral, 153. 

of lymphatics, 125. 

semilunar, 153, 158. 

tricuspid, 153. 

of veins, 161. 
Vegetable food, 58, 62. 

physiology, 9, 14, 15. 
Veins, 23, 151, 160. 

valves of, 161. 
Venae cavae, 161. 
Venous blood, 129. 
Ventilation, 141. 
Ventricles of heart, 150. 

of larynx, 294. 
Ventriloquism, 300. 
Vermicular movement, 96. 
Vertebra, 29. 
Vertebral canal, 30. 

column, 22, 29. 
Vertebrate animals, nervous system 
of, 224. 

vision in, 276. 
Vestibule, 283. 

scalae of, 285. 
Villi of intestine, 107, 121. 

of tongue, 234. 
Vision, 255. 

in inferior animals, 276. 

organ of, 256. 
Vitreous humor, 263. 



Vocal cords, 294. 

inferior or true, 294. 

superior or false, 294. 

in singing, 298. 
Voice, 293. 

in animals, 303. 

in singing, 299. 

in speaking, 299. 

intensity of, 297. 

organ of, 293. 

pitch of, 297. 

production of, 296. 

quality of, 298. 

range of, 299. 
Vowels, 302. 

Walking, 41. 

Warm-blooded animals, 179. 
Water, varieties of, 66. 
Well water as drink, 67. 
Whey, 61. 
Whiskey, 69. 
Whispering, 299. 
White of the eye, 265. 
Windpipe, 132. 
Wines, 67. 
Wisdom teeth, 77. 

Yawning, 139. 

Yellow spot of retina, 274. 




HYSIOLOGY 




■ -,s,^<- nuMmmm t MK mmm& mmmm!m mm 



